GB2249308A

GB2249308A - Purification of acetonitrile

Info

Publication number: GB2249308A
Application number: GB9023530A
Authority: GB
Inventors: Gerard Kenny; Harcourt Miles
Original assignee: G K ANALYTICAL SCIENCES LIMITE
Current assignee: G K ANALYTICAL SCIENCES LIMITE
Priority date: 1990-10-30
Filing date: 1990-10-30
Publication date: 1992-05-06
Anticipated expiration: 2010-10-30
Also published as: GB2249308B; BE1002441A6; GB9023530D0

Abstract

Feedstock acetonitrile containing impurities such as propionitrile, allyl alcohol, acetone, water, oxazole, acrylonitrile and methacrylonitrile is purified by adding the feedstock together with an oxidising agent such as potassium permanganate, adding a base to the mixture, distilling the mixture in a distillation column, and recovering purified acetonitrile from the distillation column. A very high level of purity of at least 99.8% is obtained.

Description

Solvent Purification The invention relates to solvent purification, in particular to a process for purifying acetonitrile containing impurities such as allyl alcohol, acetone, water, oxazole, acrylonitrile, methacrylonitrile, propionitrile, possibly catalytic amounts of acid and the like.

Acetonitrile was first produced commercially in 1952. It is widely used in liquid-liquid extraction, selective recrystallisation and extractive distillation. Because of its favourable dialectric, solvent and optical properties it is also widely used in analytical chemistry, particularly in high performance liquid chromatography (HPLC), DNA and peptide synthesis, pesticide residue analysis and in UV and IR spectroscopy.

As analytical chemistry techniques and machines become ever more sophisticated there is a need to develop processes for producing acetonitrile to a high level of purity for use as a standard in such machines. This invention is therefore directed towards producing acetonitrile having a high level of purity in a cost efficient manner.

According to the invention there is provided a purification process for the purification of acetonitrile containing impurities such a allyl alcohol, acetone, water, oxazole, acrylonitrile, methacrylonitrile and propionitrile to produce purified acetonitrile, the process comprising the steps of: adding an oxidising agent to acetonitrile containing impurities; adding a base to the mixture; distilling the mixture in a distillation column; and recovering purified acetonitrile from the distillation column.

In one particularly preferred embodiment of the invention the acetonitrile is further purified by adding a drying agent prior to distillation. Preferably the mixture is heated after addition of the oxidising agent. Advantageously the mixture is heated to a temperature of at least 40"C for a period of at least half an hour.

In a preferred embodiment of the invention after addition of the base the mixture is heated to reflux and the mixture is sampled over time to monitor the levels of impurities present.

In one embodiment of the invention the mixture is cooled prior to addition of the drying agent.

The invention also provides purified acetonitrile whenever purified by the process of the invention.

The invention will be more clearly understood from the following descriptions thereof given by way of example only with reference to the accompanying drawing which is a schematic diagram of a distillation apparatus used in the process of the invention.

Referring to the drawing, there is illustrated a distillation apparatus used in the process of the invention comprising a distillation column 1 of packed raschig rings having from 30 to 40 theoretical plates. Feed material is added into a boiling vessel 2 through an inlet valve 3. The feed material is heated by passing through a reboiler 5 having a steam heated coil 6. Vapour from the distillation column 1 is condensed by passing cooling water through a coil 7 in the condenser 8. Reflux material is returned to the column 1 through a reflux line 9. When the desired purity level has been reached the material is fed through an outlet line 10 through molecular sieves 11 to a collection vessel 12.

Example Feedstock acetonitrile containing impurities such as propionitrile, allyl alcohol, acetone, water, oxazole, acrylonitrile, methacrylonitrile and free ammonia was purified by the following process. 100 L of feedstock acetonitrile is added to the reflux vessel and approximately 60g of an oxidising agent such as potassium permanganate is added. A small quantity of an acid such as phosphoric acid may also be added if the level of allyl alcohol in the feedstock acetonitrile is high (i.e. > 0.01% by volume). The acid acts as a catalyst to the oxidizing agent.

The mixture is then heated for at least half and hour at a temperature of at least 400C. A base such as sodium phosphate is then added to the mixture in an amount of at least lOOg (up to 1,500g) and the mixture is heated to reflux. The levels of impurity present are monitored. When the levels of impurities have reached desired values the mixture is allowed to cool.

The final stage in the purification process involves adding a drying agent such as phosphorus pentoxide to the mixture to excess (10%) and the mixture is then heated under reflux for at least half an hour. The product is sampled and when the desired level of purity is obtained the purified acetonitrile is drawn off.

The acetonitrile purified by this process has a purity of at least 99.8% with a water content of less than 0.01%, an acidity level of less than .001% and a residue level of less than .0001%.

The high grade purified acetonitrile is useful in HPLC analysis and has a great range of applications including applications in peptide an DNA synthesis and in peptide residue analyses.

The invention is not limited to the embodiments hereinbefore described which may be varied in detail.

Claims

1. A purification process for the purification of acetonitrile containing impurities such a allyl alcohol, acetone, water, oxazole, acrylonitrile, methacrylonitrile and propionitrile to produce purified acetonitrile, the process comprising the steps of: adding an oxidising agent to acetonitrile containing impurities; adding a base to the mixture; distilling the mixture in a distillation column; and recovering purified acetonitrile from the distillation column.

2. A process as claimed in claim 1 wherein the acetonitrile is further purified by adding a drying agent prior to distillation.

3. A process as claimed in claim 1 or 2 wherein the mixture is heated after addition of the oxidising agent.

4. A process as claimed in claim 3 wherein the mixture is heated to a temperature of at least 400C for a period of at least half an hour.

5. A process as claimed in any preceding claim wherein, after addition of the base the mixture is heated to reflux and the mixture is sampled over time to monitor the levels of impurities present.

6. A process as claimed in any of claims 2 to 5 wherein the mixture is cooled prior to addition of the dehydrating and/or dealcoholising agent.

7. A process substantially as hereinbefore described with reference to the examples.

8. Purified acetonitrile whenever purified by a process as claimed in any preceding claim.