WO2009058579A1

WO2009058579A1 - Solvent process for producing brominated esters

Info

Publication number: WO2009058579A1
Application number: PCT/US2008/080144
Authority: WO
Inventors: William R. Brown; Robert C. Herndon; Bruce C. Berris
Original assignee: Albemarle Corp
Current assignee: Albemarle Corp
Priority date: 2007-11-01
Filing date: 2008-10-16
Publication date: 2009-05-07
Anticipated expiration: 2010-05-01
Also published as: TW200927723A

Abstract

Provided is a process for preparing a product useful as a flame retardant component comprised of a mixed diacetyl ester formed from tetrabromophthalic anhydride (TBPA), glycol(s), propylene oxide, and acetylating agent. The process comprises (A) reacting TBPA and glycol(s) and producing at an elevated temperature a half-ester formed from tetrabromophthalic anhydride and the glycol(s); (B) reacting half-ester with propylene oxide in the presence of a basic alkali metal salt to isopropoxylate the half-ester and (C) acetylating the isopropylated half-ester. Steps (A), (B), and (C) are performed in a liquid triaryl phosphate ester, preferably isopropylated triphenyl phosphate. Step (A) is also a process of the invention. The basic alkali metal salt used in step (B) can be added in (A) if desired.

Description

SOLVENT PROCESS FOR PRODUCING BROMINATED ESTERS

TECHNICAL FIELD [0001] This invention relates to the production of brominated glycol ester products, useful as flame retardant components.

BACKGROUND

[0002] A catalyzed, ancillary solvent-free, three-step process has been used heretofore to produce a brominated ester product from diethylene glycol (DEG), tetrabromophthalic anhydride (TBPA), propylene oxide (PO), and acetic anhydride (AA). The product, especially when suitably formulated with a liquid organic phosphate ester, is useful, as a reactive flame retardant for use in polyurethanes and related polymers.

[0003] Unfortunately, it is necessary in such solvent- free process to carry out a rather severe stripping step in order to remove from the final reaction product, the excess amount of DEG required in the process and the PO/DEG moieties formed as by-products in the process. In order to conduct such severe stripping, more complex and expensive reaction equipment is required as compared to equipment required for less severe stripping operations. Also, attempts to use in the process a common, low cost, readily- available reaction solvent such as toluene, is less advantageous because of the need to strip such a solvent from the reaction mixture before arriving at the desired final product, as such solvent would degrade the flame- retardant performance of the final product.

BRIEF SUMMARY OF THE INVENTION [0004] In one of its embodiments this invention provides a process for the production of a product comprised of a half-ester formed from tetrabromophthalic anhydride and a glycol, which preferably is diethylene glycol. This process comprises bringing together in the presence of a basic salt of an alkali metal and of a weak acid, preferably sodium carbonate, tetrabromophthalic anhydride and one or more glycols in a liquid solvent medium consisting essentially of at least one liquid triaryl phosphate ester, and producing at an elevated temperature a product comprising a major amount on a weight basis of a half-ester formed from tetrabromophthalic anhydride and at least one of the one or more glycols. The reaction mixture is proportioned such that the mole ratio of glycol(s) to tetrabromophthalic anhydride is in the range of about 1 : 1 to about 1:1.2, whereby a major amount of the product on a weight basis is the half-ester formed from tetrabromophthalic anhydride and the glycol(s), i.e., a glycol tetrabromophthalate half-ester. The prior solventless process required the mole ratio of glycols to tetrabromophthalic anhydride to be at least 1.3:1 and thus, more glycol had to be used and recovered.

[0005] In another of its embodiments this invention provides a three-step process for preparing a product comprised of a mixed diacetyl ester formed from tetrabromophthalic anhydride, at least one glycol (preferably diethylene glycol), propylene oxide, and an acetylating agent, preferably acetic anhydride. This process comprises: A) bringing together tetrabromophthalic anhydride and one or more glycols (preferably diethylene glycol) and producing at an elevated temperature a product comprising a major amount on a weight basis of a half-ester formed from tetrabromophthalic anhydride and at least one of the one or more glycols;

B) bringing together half-ester product formed in A) and propylene oxide, in the presence of a basic salt of an alkali metal and of a weak acid, preferably sodium carbonate, and producing at an elevated temperature a product comprising a major amount on a weight basis of isopropoxylated half-ester formed from tetrabromophthalic anhydride and at least one of said one or more glycols; and

C) bringing together acetic anhydride and product formed in B) comprised of isopropoxylated half-ester formed from tetrabromophthalic anhydride and at least one of said one or more glycols, and producing at an elevated temperature a product comprised of a major amount on a weight basis of mixed diacetyl ester of isopropoxylated half-ester of tetrabromophthalic anhydride and of at least one of said one or more glycols, i.e. , a product produced from tetrabromophthalic anhydride, one or more glycols (preferably diethylene glycol), propylene oxide, and acetic anhydride in the sequence described; the reactions of A), B), and C) each being conducted in a liquid solvent medium consisting essentially of at least one liquid organic phosphate ester. As in the case of the above one-step process, the glycol and tetrabromophthalic anhydride are proportioned such that the mole ratio of glycol(s) to tetrabromophthalic anhydride is in the range of about 1:1 to about 1:1.2, whereby a major amount of the product on a weight basis is the half-ester formed from tetrabromophthalic anhydride and at least one glycol. By the term "a major amount" is meant that of the total weight of reaction product mixture (excluding the weight of the solvent) more than 50 percent by weight is the specified reaction product, the balance, if any, being other reaction product(s) (again excluding the weight of the solvent present). [0006] In conducting the above three-step process, the basic salt of an alkali metal and of a weak acid that is present in the second step (i.e., in B)) can be added during the conduct of step A) or at the beginning of the second step or, if desired, it can be added as a component of the first step reaction mixture (i.e., it can be added so that it is present when the reaction in step A) is initiated) so that it is carried over into the reaction mixture of the second step where it exerts its function of assisting in the opening of the propylene oxide ring. [0007] The above and other embodiments and features of this invention will become still further apparent from the ensuing description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. 1 is an idealized representation of the above one-step process for producing a half-ester of TBPA and glycol(s), the depiction in this case being an idealized representation of the preferred process of forming the half-ester product of TBPA and DEG. [0009] Fig. 2 is an idealized representation of steps 1 and 2 of the above three-step process, the depiction in this case being an idealized representation of preferred steps 1 and 2, wherein TBPA and DEG are used as reactants in the first step and propylene oxide is used as areactant in the second step.

[0010] Fig. 3 is an idealized representation of step 3 of the above three-step process, the depiction in this case being an idealized representation of preferred step 3, wherein acetic anhydride is used as a reactant in the third step in order to form the desired reaction product comprised of a mixed diacetyl ester formed from TBPA, DEG, propylene oxide, and acetic anhydride.

[0011] The formulas used in Figs. 1-3 are not intended to depict molecules in accordance with their three-dimensional spatial configurations. Instead, the molecules are depicted schematically using conventional chemical depictions.

FURTHER DETAILED DESCRIPTION OF EMBODIMENTS OF THIS

INVENTION

[0012] Throughout the specification and claims hereof, reference is made to half-esters "formed from". This expression is intended to identify the components used in the reaction which produces the half-ester product. These expressions are not intended to identify the reaction mechanism(s) involved or to identify the precise chemical species that enter into the reaction(s) forming the half-ester. [0013] A feature of the present invention is that the one-step and the three-step process both use a liquid phosphate ester solvent or diluent in order to keep the reaction mixture fluid, while lowering the mole ratio of DEG to TBPA to about 1.06: 1 from the mole ratio of 1.31 : 1 required in the diluent- free process. [0014] Any inert liquid triaryl phosphate ester or mixture thereof can be used as the solvent/diluent in the one-step and three-step processes of this invention. A few non-limiting examples of such solvent/diluents include cresyl diphenyl phosphate, tricresyl phosphate, trixylyl phosphate, liquid alkylated triphenyl phosphate mixtures (e.g., mixtures of ethylated triphenyl phosphates, mixtures of propoxylated triphenyl phosphates, mixtures of butylated triphenyl phosphates), liquid phosphorylated alkyl phenol/phenol ester mixtures, and similar liquid triaryl phosphate compounds or mixtures. Methods for the preparation of such materials are known and are reported in the literature. See, for example, U.S. Pat. Nos. Re.29,540, 4,139,487, 4,351,780, 5,206,404, and 7,153,901. Preferred liquid triaryl phosphate esters for use in the practice of the one-step and three-step processes of this invention are isopropylated triphenyl phosphate ester products (also known as triaryl phosphate isopropylated products). Such preferred products are presently available commercially as Phosflex^® 3 IL flame retardant plasticizer (Supresta LLC) and as Reofos^® 35, Reofos^® 50, Reofos^® 65, and Reofos^® 95 (Chemtura Corporation). Typical properties as given by the manufacturer for Phosflex^® 3 IL are as follows:

Physical Appearance Clear, Transparent Liquid Phosphorus Content 8.3 wt%

Specific Gravity 1.179 at 20°C/20°C

Density at 20⁰C 9.84 lbs/gal; 1179 kg/m³

Viscosity at 25°C 60 mPa.s

Acidity 0.10 mg KOH/g Water Content 0.10 wt%

Color, APHA <75

[0015] Any of a wide variety of glycols can be used in the one-step and three-step processes of this invention. Typically, use is made of aliphatic glycols such as ethylene glycol, propylene glycol, 1,4-butylene glycol, neopentyl glycol, diethylene glycol, triethylene glycol, dipropylene glycol, analogous liquid glycols, and mixtures of two or more such materials. The preferred glycol reactant for use in the processes of this invention is diethylene glycol. [0016] Any of a wide variety of basic salts of an alkali metal and a weak acid can also be used in the one-step and three-step processes of this invention. Such salts serve the role of forming a catalyst system in the reaction medium that facilitates the reaction in the one-step reaction or in the first step of the three-step reaction. In addition, depending upon the process used to form the tetrabromophthalic anhydride, small amount of acid, e.g. , sulfuric acid, may be present as an impurity in this compound. Thus, besides engendering catalytic activity, such basic alkali metal salts also serve to neutralize any such acid that may be present in the tetrabromophthalic anhydride.

[0017] The function of the alkali metal salt is to catalyze the reaction of propylene oxide with the carboxylic acid moieties formed in step 1. The presence of the residues of the alkali metal salt in steps 1 and 3 of the three-step process does not interfere with the reactions occurring in steps 1 and 3, and thus presents no difficulty. Non-limiting examples of such basic alkali metal salts include alkali metal carbonates (e.g., lithium carbonate, sodium carbonate, potassium carbonate), alkali metal bicarbonates (e.g., sodium bicarbonate, potassium bicarbonate), alkali metal acetates (e.g., sodium acetate, potassium acetate, lithium acetate, rubidium acetate), alkali metal propionates (e.g., sodium propionate, potassium propionate), and other similar basic alkali metal salts. Mixtures of two or more basic alkali metal salts can be used. Preferred for use in the practice of this invention are basic sodium salts of weak acids, especially sodium carbonate, as these substances are not only highly effective, but, in certain end use applications of the final product, the presence of potassium rather than sodium can be undesirable.

[0018] In conducting a three-step process in accordance with this invention, it is possible to use fresh liquid aryl phosphate ester in each of the three steps. However, a feature of this invention is that the liquid aryl phosphate ester(s) employed in the first stage can remain in the reaction mixtures of the second and third steps and thus can be effectively utilized throughout the entire three-step reaction process. In this connection, the use of isopropylated triphenyl phosphate is preferred because the resultant product of the three-stage reaction is sold in the marketplace as a solution in isopropylated triphenyl phosphate which solution is formed by dissolving the product formed in a solvent-free process with isopropylated triphenyl phosphate. Thus, in accordance with this invention, the resultant product from the three-stage process already contains some isopropylated triphenyl phosphate and thus, besides achieving the benefits in the process itself resulting from the utilization of isopropylated triphenyl phosphate as the preferred reaction solvent/diluent throughout the entire reaction process, the presence of this solvent/diluent in the final reaction product minimizes the amount of additional isopropylated triphenyl phosphate required to formulate the commercial flame retardant product. [0019] While this invention is applicable to the preparation of various end products depending upon the particular glycol(s) and liquid phosphate ester used, the temperatures referred to in the following discussion illustrate the invention with particular reference, in the one-step process and in the first step of the three-step process of diethylene glycol as the glycol reactant and an isopropylated triphenyl phosphate as the solvent in at least the first step and preferably all three steps of the three-step process. When glycol(s) other than diethylene glycol and/or liquid triaryl phosphate ester(s) other than isopropylated triphenyl phosphate are used, the temperatures given in the ensuing description for reactions in which diethylene glycol and isopropylated triphenyl phosphate are used serve as a convenient starting point for determining optimum temperature conditions for use with the particular glycol(s) and/or liquid triaryl phosphate(s) being used. In short, all that is required is to perform a few preliminary small scale laboratory experiments in order to develop the optimum temperatures for use in the one-step and three-step processes of this invention in which use is made of glycol(s) other than diethylene glycol and/or liquid triaryl phosphate(s) other than isopropylated triphenyl phosphate. [0020] The preferred intermediate product is a solution of the half-ester product formed from tetrabromophthalic anhydride and diethylene glycol in a liquid triaryl phosphate ester, more preferably an isopropoxylated triphenylphosphate ester. The preferred end product is a solution of a brominated ester product formed from tetrabromophthalic anhydride, diethylene glycol, propylene oxide, and acetic anhydride in a liquid isopropoxylated triphenylphosphate ester. The preferred intermediate product is formed in a process which, in the above three- step process, is formed in the first step and used as a reactant in the second step of the three- step process, which process results in the third step of the process in the production of the preferred end product. [0021] In the one-step processes of this invention and in the first step of the three-step processes of this invention for preparing a solution of the half-ester product from tetrabromophthalic anhydride and diethylene glycol in a liquid triaryl phosphate ester, more preferably in an isopropoxylated triphenylphosphate ester, the reaction is typically conducted at an elevated temperature in the range of about 120⁰C to about 150⁰C, and preferably in the range of about 125°C to about 140⁰C in a reactor equipped with a condenser, nitrogen inlet, agitator, and temperature controller. Although other modes of addition may be used, it is preferred to add the tetrabromophthalic anhydride to a preformed mixture of (i) the diethylene glycol and (ii) the basic salt(s) of an alkali metal and a weak acid. Such addition is typically conducted (a) on a sufficiently slow portionwise basis, or (b) on a sufficiently slow continuous basis, or (c) as a concurrent or sequential combination of (a) and (b), that in any such case maintains the reaction mixture in a fluid state. By a concurrent combination of (a) and (b) is meant that two feeds are being conducted concurrently, one of which is a feed as in (a) and one which is as a feed in (b). By the term "fluid state" is meant that the resultant mixture is similar to a fluid with a viscosity of 500 cP.

[0022] Typically, upon completion of the feed of the tetrabromophthalic anhydride, the reaction mixture is maintained at a suitably elevated temperature (e.g., about 125°C to about 140⁰C) with agitation for a suitable ride period which varies, to some extent, depending upon the scale of operation. Ordinarily the ride period, if used, is at least about one hour and, as noted, can be longer.

[0023] In the three-step processes of this invention, the first step is as described above in connection with the one-step processes of this invention.

[0024] The second step of the three-step processes of this invention is typically conducted in the same reactor on completion of the first-step reaction including the ride period, if used. However, the reaction can be allowed to stand longer or can be transferred to another reactor in which the second step is conducted, should this be desired. In the second step, the propylene oxide is added portionwise or very slowly, but continuously, to reaction mixture formed in the first step. When the glycol used in the first step is diethylene glycol, the reaction mixture is typically at an elevated temperature in the range of about 115⁰C to about 130⁰C. If this reaction is carried out at about atmospheric pressure, the consequent refluxing of the mixture tends to reduce the temperature somewhat. The reaction is an exothermic reaction, however. Thus, it is desirable to maintain the temperature either by cooling or by regulating the feed rate of propylene oxide, or both, so that the temperature remains in the range of about 115°C to about 130⁰C. A preferred temperature range for this second step reaction is about 120⁰C to about 125°C. The amount of propylene oxide charged in any given plant operation is best determined at the outset by taking periodic representative samples of the reaction mixture during the propylene oxide addition to determine the acid number of the reaction mixture. The addition should continue until the acid number reaches about 0.2 and preferably less than 0.2. Ordinarily, the lower the acid number of the reaction mixture, the better. However, practical considerations may indicate that attempts to achieve extremely low acid numbers in step 2 (e.g., values below 0.05) can become economically impracticable. Thus, after performing a few preliminary test operations such as in a pilot plant, the amount and rate of propylene oxide addition to a given quantity of a product from step 1 can be determined and thereafter the operational procedure can be set so that it is no longer necessary to make acid number measurements during regular plant operations, except for possible periodic measurements to ensure that product of specification quality is being produced. Another desired feature of the product from step 2 is that the bromine content of such product be at least 43.5 wt% or above. This ensures that the final product from stage 3 will have a high enough bromine content to meet desirable end product specifications. [0025] In step 3 of the three-step process, acetic anhydride is added to reaction product formed in step 2. Once again, it is preferred to carry out step 3 in the same reactor as steps 1 and 2, as this tends to reduce capital costs and tends to facilitate the overall operation. However, the reaction mixture can be transferred to another reactor in which the third step is to be conducted, should this be desired. Whichever system is used, the third step should be conducted with a distillation head cooled to a temperature of about 15 to 25⁰C to avoid freezing the acetic acid. Thus, if the reaction of step 3 is conducted in the same reaction vessel as steps 1 and 2, the condenser should be replaced with a suitable distillation head. In step 3, acetic anhydride is added portionwise or very slowly, but continuously, to reaction mixture formed in the second step. The reaction mixture is typically at an elevated temperature in the range of about 115°C to about 135°C, and preferably in the range of about 120⁰C to about 130⁰C. The total amount of acetic anhydride charged should be such as to produce a reaction product mixture in which the hydroxyl number is 20 or less. Standard titration methods or spectroscopic measurements can be used to determine hydroxyl number. [0026] The acid number of the product should be about 0.2, and preferably less than 0.2, the acid number considerations being essentially the same as those described above in connection with step 2 of the three-step process. If the acid number of the product remains significantly above about 0.2, additional stripping of the reaction mixture at up to about 150⁰C and a vacuum of about 5 mm Hg or less should lower the acid number to the desired level. If this cannot be accomplished, propylene oxide should be introduced into the reaction mixture in order to reduce the acid number to the appropriate level.

[0027] Other acetylating agents, such as acetyl chloride, can be used in lieu of acetic anhydride. However, acetic anhydride is the preferred acetylating agent. [0028] In the three-step process, the three steps as described above (in some cases identified as A), B), and C)) can be implemented with additional steps if deemed necessary or desirable.

Thus, the designations first step, second step, and third step do not denote that the steps must be conducted without any intermediate steps or operations. For example, after the first step or

A), the reaction mixture can be allowed to stand so that it cools, such as to room temperature.

The reaction can then be reheated to the reaction temperature used for conducting the second step or B). In addition, or alternatively, the reaction product from the first step may be treated to remove at least some impurities, if desired. Similarly, after conducting the third step or C), volatile components can be removed from the product formed in the third step, such as by use of vacuum distillation. Also, as noted above, the product from the third step can then be blended with additional liquid triaryl phosphate ester, especially isopropylated triphenyl phosphate in order to produce a very desirable flame retardant product containing about 50 to about 65 percent by weight of isopropylated triphenyl phosphate and having a bromine content in the range of about 14 to about 26 weight percent. If any solids are present in the product formulation, these can be removed by any convenient solids-liquid physical separation procedure such as filtration. The typical specifications for a very desirable product of this type are as follows: acid number, 0.20 maximum; water content, 0.20% maximum; bromine content, 40% minimum.

[0029] If this reaction is carried out at about atmospheric pressure, the consequent refluxing of the mixture tends to reduce the temperature somewhat. The reaction is an exothermic reaction, however. Thus, it is desirable to maintain the temperature either by cooling or by regulating the feed rate of propylene oxide, or both, so that the temperature remains in the range of about 115°C to about 130⁰C. A preferred temperature range for the second step reaction using diethylene glycol and tetrabromophthalic anhydride as reactants in the first step, and propylene oxide and reaction product formed in the first step as reactants in the second step, is about 120⁰C to about 125°C. The amount of propylene oxide charged in any given plant operation is best determined at the outset by taking periodic representative samples of the reaction mixture during the propylene oxide addition to determine the acid number of the reaction mixture. The addition should continue until the acid number reaches about 0.2 and preferably less than 0.2. Ordinarily, the lower the acid number of the reaction mixture, the better. However, practical considerations may indicate that attempts to achieve extremely low acid numbers in step 2 (e.g., values below 0.05) can become economically impracticable. Thus, after performing a few preliminary test operations such as in a pilot plant, the amount and rate of propylene oxide addition to a given quantity of a product from step 1 can be determined and thereafter the operational procedure can be set so that it is no longer necessary to make acid number measurements during regular plant operations, except for possible periodic measurements to ensure that product of specification quality is being produced. Another desired feature of the product from step 2 is that the bromine content of such product be at least 43.5 wt% or above. This ensures that the final product from stage 3 will have a high enough bromine content to meet desirable end product specifications. [0030] Referring now to the drawings, it can be seen from Figs. 1 and 2 that in the one-step process of this invention (Fig. 1), and in the first step of the three-step process of this invention (Fig. 2), tetrabromophthalic anhydride, e.g., available commercially as Saytex^® RB- 49, reacts with DEG to form the half-ester. This is reacted directly in step 2 of the three-step process with propylene oxide (PO) to form an intermediate product. Note Fig. 2. The reaction of step 2 is exothermic and, depending upon reaction scale and feed rates employed, external cooling may be required. It is preferred to feed the PO into the reactor via a dip tube that extends below the surface of the reaction mixture. Care must be taken to ensure that the reaction mixture cannot back up into the PO supply. If the PO is fed above the surface of the reaction mixture, then sufficient agitation is required to ensure that the gas in the headspace is drawn into the reaction mixture. It is preferred that the reactor be blocked in to prevent the escape of PO vapors. If the PO feed vessel is operated at a nominal 40 to 50 psig then the reactor will rarely experience a pressure greater than about 45 psig although most commercial operations typically employ an upper limit of 35 psig PO pressure as a safety precaution.

[0031] The reaction scheme shown is an idealized representation of the mixture of products formed. In reality, the process is much more complicated. For example, in step 1 of the preferred one-step reaction and in the first step of the preferred three-step process, one molecule of DEG can react with one or two molecules of RB-49 (rather than simply one as shown) to form the half-ester, or dimer (1), and higher oligomers such as 2 can then be formed from 1. See in this connection Fig. 3, which depicts the structures of higher oligomers 1 and 2. Furthermore, PO can react with these acid-esters at both the alcohol and acid sites, and form secondary or primary alcohols by opening the PO in different orientation. Also, multiple additions of PO at each site can occur. In this way, the actual, final product is typically composed of at least about 20 distinct components. [0032] In the third step of the preferred three-step process of this invention (note Fig. 3), the relative amount of acetic anhydride reacted with the product from the second step should be just a slight deficiency such that a small percentage of the free hydroxyl functionalities remain unconverted to acetyl esters. Excess acetic anhydride can cause the product to have a high acid number. The by-product acetic acid is stripped off under vacuum leaving a product possessing a slight acidity. The acid number following the strip should be less than 5. Another treatment with a small amount of PO may be needed to bring the acid number below 0.15.

[0033] If a higher vacuum is available or achievable, it should be used to speed the stripping process. There is no risk of distilling over the product, except by splashing or bumping. [0034] The stripping steps are straightforward. The second step reaction mixture tends not to foam unless fairly extreme conditions are experienced whereas the third step reaction product may show a slight tendency to foam if the vacuum is applied too quickly. Increased temperatures may shorten the cycle time but the maximum allowable value is not known at this time. Unless indicated by preliminary tests using the reactants proposed for use in a given operation, the strip temperature should not be greater than about 160⁰C. [0035] The second step and third step products will be clear amber in appearance and quite viscous at room temperature. Care should be taken to ensure that the hot product is not exposed to air/oxygen due to the potential for the product to be oxidized and darken substantially. A system of checks should be in place to ensure that cross contamination does not occur and that the highest probability types of contamination (i.e. water washes of vessels) be detected by the analytical methods employed.

[0036] The suggested amounts of raw materials used in the preferred three-step process of this invention assuming use of a 2000-gallon batch reactor will now be described. The suggested amounts of raw materials used in steps 1 and 2 are shown in Table 1.

Table 1

[0037] Venting and stripping at 30 mm Hg and 160⁰C should remove 145 to 160 kg of volatiles, mainly PO and its dimers.

[0038] The product formed in the second step typically has a hydroxyl number of 151, a bromine content of 43.8 wt%, and an acid number of less than 0.10. To this product is added 2110 kgs of acetic anhydride in step 3. Thereafter, 21 kg of propylene oxide can be employed as makeup in order to adjust acid number. A byproduct of 1351 lbs of acetic acid is obtained. Estimated amount of desired end product in a properly conducted three-step process of this invention (prior to the preferred addition of more isopropylated triphenyl phosphate) should be in the order of about 8900 kg. [0039] A detailed process procedure for use in conducting the above preferred three-step process using a 2000-gallon batch reactor is as follows:

[0040] 1 ) Start with a clean, dry, and nitrogen-blanketed reactor. For subsequent batches, cleaning is not needed. [0041] 2) Charge isopropylated triphenyl phosphate, DEG and Na₂CO₃ to the reactor under a nitrogen atmosphere. Purge with nitrogen if needed, e.g., if the reactor has been opened, and heat to 135°C.

[0042] 3) Add the tetrabromophthalic anhydride (TBPA) at a rate sufficient to maintain the reaction temperature above 130⁰C. The heat of reaction for this step has been measured to be about 5 kcal/g mol but the temperature is observed to drop with each addition because of the heat of dissolving and the cooling effect of the solid being at ambient temperature. The addition of TBPA is carried out over a 1 hour time period at the bench scale. At the 2000- gallon batch scale, it may take longer, depending on the heat transfer rate and the ability to transfer supersacks of the TBPA. If the addition is done too rapidly, the reaction mixture could cool to 120⁰C, at which temperature solid could precipitate. [0043] 4) Allow the mixture to cook for 1 hour at 135°C after the TBPA addition is complete.

[0044] 5) Begin feeding propylene oxide (PO) over a 3 to 5-hour period initially maintaining the reaction temperature at 135°C. The temperature should be allowed to gradually drop to 120°C after about 25% of the PO charge has been added. The temperature must not be lowered too soon, because the mixture may freeze. Failure to lower the temperature during the PO feed will increase the PO utilization. Cycle time will be dependent on heat transfer. In lab runs at atmospheric pressure (efficient reflux condenser at 0⁰C), the PO feed required 3-4 hours . The heat of reaction for the PO addition is estimated to be at least 12.5 kcal/g mole of PO.

[0045] 6) Table 1 gives typical laboratory scale PO utilization at atmospheric pressure. At the larger scale under discussion, the PO utilization may be lower or higher depending on many factors. For the initial batches, one should charge only about 90% of the amount listed in the Table. Then, allow the reaction mixture to cook for 30 minutes at 120°C and determine the acid number for the product. If the acid number is greater than 0.15, add more PO, hold 30 minutes and recheck the value. This operation is repeated until the acid number is in the desired range. The PO utilization experience in the first few batches can then be used to determine how much PO to feed in subsequent runs. The theoretical makeup PO charge is found from the following: kgs PO to add = wt of reactor contents (in kgs) x acid number x 0.001035 Because PO does not react in exact proportion to the remaining acid (some of it growing onto hydroxyl terminated chains), more than the theoretical amount of PO will be required. This can only be determined by experiment since it depends on agitation, rate of addition, pressure, reactor geometry and its headspace. Once repeated runs give confidence in the amount of PO charge, make-up charges may be found to be unnecessary, with the required amount added continuously. The PO should be added very slowly at the end of the charge, even when the temperature is adequately controlled. [0046] 7) Upon attaining the desired acid number, the mixture is stripped of volatiles at 120 to 160°C and 30 mm Hg vacuum or less. As much volatile material should be removed as possible. The distillate mass is 145 kg scaled to 5000 kg of TBPA. The approximate composition of the distillate is:

PO 53% dimethyldioxane 36 (2 isomers) methylethyldioxolane 11 (2 isomers) [0047] 8) After stripping the mixture a sample is taken for acid and hydroxyl numbers. [0048] 9) A desirable target for the end product from step 3 is a hydroxyl number of 10. Calculate the acetic anhydride charge as follows: kgs of Acetic Anhydride = (OH number of step 2 product - desired OH number) x (kgs of step 2 product) x 0.00182 For example, with 7778 kgs of step 2 product with an OH number of 131, a target residual OH number of 10 in the step 3 product, the acetic anhydride charge would be 1719 kgs.

[0049] 10) Add the acetic anhydride at 120⁰C. Addition normally takes 1 to 3 hours, but may take longer depending on the heat transfer rate. The reaction is exothermic. Near the end of the acetic anhydride addition the reaction temperature will begin to drop and heating is applied to maintain the reaction temperature at about 120⁰C. [0050] 11) Cook the mixture for one hour at 120⁰C after the anhydride addition is complete.

[0051] 12) Strip the acetic acid by-product by reducing the pressure in the reactor slowly. The product has a tendency to foam if vacuum is applied too quickly. To avoid plugging the condenser, it must be at higher than 16°C, the mp of acetic acid.

[0052] 13) Ending conditions for the strip are a temperature of 160⁰C at a pressure of 30 mm Hg. If the equipment is capable, the final pressure may be lower, and/or a nitrogen sparge used to improve the strip rate. [0053] 14) The acid number of the product is determined. If the acid value is greater than

5, resume stripping. If the value is between 5 and 0.15, PO is added at 100⁰C to 120⁰C. The PO charge is calculated from: kgs PO to add = wt of reactor contents (in kgs) x acid number x 0.001035 [0054] 15) The mixture is then cooked for 30 minutes following the PO addition before sampling. If necessary, additional PO may be added to achieve the desired acid number.

[0055] 16) If a PO neutralization is needed then the mixture must be stripped of residual PO once the desired acid number is obtained. This final strip should be conducted at a temperature of 160⁰C at 30 mm Hg in order to remove volatile compounds and to increase the product bromine content to >37.5 wt%.

[0056] 17) After the final PO strip a sample is taken for complete analytical evaluation. Typical Step Three Product Specifications

Acid Number 0.20 max

Hydroxyl Number 25 max

Water 0.1% max

Br 37.6% min Phosphorus 0.73% typical

The bromine content, density and viscosity will depend on the initial isopropylated triphenyl phosphate charge.

[0057] Evaluations of product formed by the three-step process of this invention when conducted on a laboratory scale indicated that the product is at least as good as product previously produced by the more complex and expensive solvent-free process.

[0058] The following Example is presented for purposes of illustration and not of limitation of the generic scope of the invention.

EXAMPLE [0059] A 3-liter, 4-necked flask with condenser, nitrogen inlet, agitator, thermometer and temperature controller was purged with nitrogen, and then charged with 414 grams (3.91 mol) of diethylene glycol, 265 grams of isopropylated triphenyl phosphate (IPPP), and 4.00 grams (37.7 mmol) of anhydrous granular sodium carbonate. This mixture was heated to 120⁰C, where addition of tetrabromophthalic anhydride (1,681 grams, 3.63 mol) was begun. The temperature was raised to 138°C during the addition, which took 40 min. After one hour at

135 to 138°C, addition of propylene oxide was begun. An efficient condenser was used though which coolant at 4°C was passed. The reaction mixture temperature was gradually lowered during the addition of the first 100 grams to 120⁰C and held there for the remaining portion of the propylene oxide feed. A total of 388 grams of propylene oxide was added, and the mixture was then held at 120⁰C for 45 min. A sample was drawn and titrated to determine the acid number, which was less than 0.05. Excess propylene oxide and other volatiles (46 grams) were removed in a vacuum at 100 to 120⁰C. A sample drawn at this point had an acid number of <0.01, bromine 43.8%, and a hydroxyl number of 151. The reaction mixture was allowed to cool overnight.

[0060] The mixture was gradually heated back to 120⁰C, and the condenser was replaced with a distillation head and cooled to 15°C. To the reaction mixture was added 707 grams (6.93 mol) acetic anhydride over a 3-hour period. After heating to 120⁰C for one more hour, acetic acid by-product was removed by vacuum distillation at 120⁰C, slowly lowering the pressure to avoid foaming. Stripping was continued until the vacuum was 9 mm Hg, and the temperature was raised to 160⁰C. A sample was drawn and titrated giving an acid number of 0.44. After lowering the temperature to 120⁰C, 2.4 grams of propylene oxide was added and the reaction mixture was held at 120⁰C for 2 hours. A sample was titrated giving an acid number of 0.11. Volatile components were removed at 92°C and 3 mm Hg vacuum. [0061] The product can be formulated with additional IPPP and filtered to remove a small amount of insolubles before use. [0062] Although any reliable standard method can be used for determining acid number, the following procedure is recommended for use. A sample of 3 grams is drawn and weighed accurately, and dissolved in 7 grams of acetone. One drop of a 10 % α-naphtholbenzein solution in acetone is added, and a yellow color is observed. To this is added with stirring 0.1 N NaOH in water until the blue color is just visible and persistent after 30 seconds of stirring. The acid number is determined by the expression: acid number = (mL of titrant x normality of titrant x 56.1) divided by the sample weight in grams

[0063] Additional embodiments of this invention include the following: a) A process for preparing a product comprised of a mixed diacetyl ester formed from tetrabromophthalic anhydride, at least one glycol, propylene oxide, and an acetylating agent, which process comprises bringing together in a liquid solvent medium consisting essentially of at least one liquid organic phosphate ester, (1 ) acetic anhydride and (2) a product comprised of isopropoxylated half-ester formed from tetrabromophthalic anhydride and at least one of one or more glycols, and producing at an elevated temperature a product comprised of a major amount on a weight basis of mixed diacetyl ester of isopropoxylated half-ester formed from tetrabromophthalic anhydride and at least one of said one or more glycols. This reaction, when using diethylene glycol as the glycol, is depicted as the principal reaction of step 3 in Figure 3. b) A process as in a) wherein said product comprised of isopropoxylated half-ester formed from tetrabromophthalic anhydride and at least one of one or more glycols is formed by bringing together in a liquid solvent medium consisting essentially of at least one liquid organic phosphate ester (i) propylene oxide and (ii) a half-ester formed from tetrabromophthalic anhydride and at least one glycol. This reaction, when using diethylene glycol as the glycol, is depicted as step 2 in Figure 2.

[0064] Typically, the glycols used contain up to about 10 carbon atoms in the molecule. [0065] Components referred to by chemical name or formula anywhere in the specification or claims hereof, whether referred to in the singular or plural, are identified as they exist prior to coming into contact with another substance referred to by chemical name or chemical type (e.g., another component, a solvent, or etc.). It matters not what chemical changes, transformations and/or reactions, if any, take place in the resulting mixture or solution as such changes, transformations, and/or reactions are the natural result of bringing the specified components together under the conditions called for pursuant to this disclosure. Thus the components are identified as ingredients to be brought together in connection with performing a desired operation or in forming a desired composition. Also, even though the claims hereinafter may refer to substances, components and/or ingredients in the present tense ("comprises", "is", etc.), the reference is to the substance, component or ingredient as it existed at the time just before it was first contacted, blended or mixed with one or more other substances, components and/or ingredients in accordance with the present disclosure. The fact that a substance, component or ingredient may have lost its original identity through a chemical reaction or transformation during the course of contacting, blending or mixing operations, if conducted in accordance with this disclosure, matters not. [0066] Except as may be expressly otherwise indicated, the article "a" or "an" if and as used herein is not intended to limit, and should not be construed as limiting, a claim to a single element to which the article refers. Rather, the article "a" or "an" if and as used herein is intended to cover one or more such elements, unless the text expressly indicates otherwise. [0067] Each and every patent or publication referred to in any portion of this specification is incorporated in toto into this disclosure by reference, as if fully set forth herein.

[0068] This invention is susceptible to considerable variation in its practice. Therefore the foregoing description is not intended to limit, and should not be construed as limiting, the invention to the particular exemplifications presented hereinabove.

Claims

CLAIMS:

1. A process for the production of a product comprised of a half-ester formed from tetrabromophthalic anhydride and one or more glycols, which process comprises bringing together in the presence of a basic salt of an alkali metal and of a weak acid, tetrabromophthalic anhydride and one or more glycols in a liquid solvent medium consisting essentially of at least one liquid triaryl phosphate ester, to thereby form a reaction mixture proportioned such that the mole ratio of glycol(s) to tetrabromophthalic anhydride is in the range of about 1:1 to about 1:1.2, and producing at an elevated temperature a product comprising a major amount on a weight basis of a half-ester formed from tetrabromophthalic anhydride and at least one of said one or more glycols.

2. A process as in Claim 1 wherein said liquid triaryl phosphate ester is an isopropylated triphenyl phosphate.

3. A process as in Claim 1 wherein said liquid triaryl phosphate ester is an isopropylated triphenyl phosphate and wherein said glycol is diethylene glycol.

4. A process as in Claim 1 wherein the tetrabromophthalic anhydride is added to a preformed mixture in said liquid solvent medium of (i) the glycol(s) and (ii) the basic salt of an alkali metal and of a weak acid.

5. A process as in Claim 4 wherein the tetrabromophthalic anhydride is added to said preformed mixture (a) on a sufficiently slow portionwise basis, or (b) on a sufficiently slow continuous basis, or (c) as a concurrent or sequential combination of (a) and (b), that in any such case maintains the reaction mixture in a fluid state.

6. A process as in Claim 4 wherein said liquid triaryl phosphate ester is an isopropylated triphenyl phosphate, wherein said glycol is diethylene glycol,and wherein said basic salt is sodium carbonate.

7. A process as in Claim 4 wherein said elevated temperature is in the range of about 120⁰C to about 150⁰C.

8. A process as in Claim 6 wherein said elevated temperature is in the range of about 125°C to about 140⁰C.

9. A process for preparing a product comprised of a mixed diacetyl ester formed from tetrabromophthalic anhydride, at least one glycol, propylene oxide, and an acetylating agent, which process comprises: A) bringing together tetrabromophthalic anhydride and one or more glycols and producing at an elevated temperature a product comprising a major amount on a weight basis of a half-ester formed from tetrabromophthalic anhydride and at least one of said one or more glycols; B) bringing together half-ester product formed in A) and propylene oxide, in the presence of a basic salt of an alkali metal and of a weak acid, and producing at an elevated temperature a product comprising a major amount on a weight basis of isopropoxylated half-ester formed from tetrabromophthalic anhydride and at least one of said one or more glycols; and C) bringing together acetic anhydride and product formed in B) comprised of isopropoxylated half-ester formed from tetrabromophthalic anhydride and at least one of said one or more glycols, and producing at an elevated temperature a product comprised of a major amount on a weight basis of mixed diacetyl ester of isopropoxylated half-ester formed from tetrabromophthalic anhydride and at least one of said one or more glycols; the reactions of A), B), and C) each being conducted in a liquid solvent medium consisting essentially of at least one liquid organic phosphate ester.

10. A process as in Claim 9 wherein the tetrabromophthalic anhydride is added to a preformed mixture of (i) the glycol(s),(ii) the basic salt of an alkali metal and of a weak acid, and (iii) said liquid solvent medium.

11. A process as in Claim 9 wherein the tetrabromophthalic anhydride is added to a preformed mixture of the glycol(s) and said liquid solvent medium, and wherein during and/or after conducting step A), the basic salt of an alkali metal and of a weak acid is added as one of the components brought together for step B).

12. A process as in Claim 9 wherein the tetrabromophthalic anhydride is added to a preformed mixture of (i) the glycol(s),(ii) the basic salt of an alkali metal and of a weak acid, and (iii) said liquid solvent medium (a) on a sufficiently slow portionwise basis, or (b) on a sufficiently slow continuous basis, or (c) as a concurrent or sequential combination of (a) and (b), that in any such case maintains the reaction mixture in a fluid state.

13. A process as in Claim 9 wherein said liquid triaryl phosphate ester is an isopropylated triphenyl phosphate.

14. A process as in Claim 13 wherein said glycol is diethylene glycol.

15. A process as in Claim 13 wherein said elevated temperature in A) is in the range of about 120⁰C to about 150⁰C.

16. A process as in Claim 14 wherein said basic salt is sodium carbonate.

17. A process as in Claim 16 wherein said elevated temperature is in the range of about 125°C to about 140⁰C.

18. A process as in Claim 9 wherein:

> the tetrabromophthalic anhydride is added to a preformed mixture of (i) the glycol(s),(ii) the basic salt of an alkali metal and of a weak acid, and (iii) said liquid solvent medium;

> said liquid triaryl phosphate ester is an isopropylated triphenyl phosphate;

> said glycol is diethylene glycol; and

> said elevated temperature in A) is in the range of about 120⁰C to about 150⁰C.

19. A process as in Claim 18 wherein said basic salt is sodium carbonate.

20. A process as in Claim 9 wherein:

> the tetrabromophthalic anhydride is added to a preformed mixture of (i) the glycol(s),(ii) the basic salt of an alkali metal and of a weak acid, and (iii) said liquid solvent medium

(a) on a sufficiently slow portionwise basis, or (b) on a sufficiently slow continuous basis, or (c) as a concurrent or sequential combination of (a) and (b), that in any such case maintains the reaction mixture in a fluid state;

> said liquid triaryl phosphate ester is an isopropylated triphenyl phosphate;

> said glycol is diethylene glycol;

> said basic salt is sodium carbonate; and > said elevated temperature in A) is in the range of about 125°C to about 140⁰C.