CA2195019A1 - Use of benzaldehydes to mark hydrocarbons - Google Patents

Abstract

The invention relates to the use of benzaldehydes of the formula (I), in which ring A can be benzo-anellated and R1, R2 and R3 are hydrogen, hydroxy, C1-C15 alkyl, C1-C15 alkoxy, cyano, nitro or a radical of the formula NR4R5 or COOR6, in which R4 is hydrogen or possibly substituted C1-C15 alkyl, R5 is possibly substituted C1-C15 alkyl or a radical of the formula L-NX1X2, in which L is C2C8 alkylene and X1 and X2 are mutually independently C1-C6 alkyl or, together with the nitrogen atom bonding them, a heterocyclic radical, and R6 is hydrogen, possibly substituted C1-C15 alkyl or a radical of the formula LNX1X2, in which L, X1 and X2 have the above meanings, as marking agents for hydrocarbons, a process for detecting these benzaldehydes in hydrocarbons and hydrocarbons containing the above benzaldehydes.

Description

~ 2~ 9501 9 Use o~ b~ hydes for marking LydL~L~o~s ~he preDent invention rel-t ~ to the u-e of b~n7~ 'yd-~ o~ t~e 5 form~l~ I

C ~ (I) 15 in which the ring A may be ~_,zo~u,Ld, and ~l, RZ and R3 are each, i , ly o~ o~e anor~er~ hydrogen, hydroxyl, Cl-Cl~- lkyl, C1-C1~-alkoxy~ cyano, nitro or a r~dic~l Or thu formula ~R~R5 or cooR5 where R~ is hydrogen or C1-C15-alkyl wlth or without interruption by ~rom 1 to 4 oxygen atoml in ether function and with a without sub~titution by phenyl~
RS is C1-Cls-~lkyl with or without iut~L~u~Llon ~y rrom 1 to 4 oxygen atomL in ether f unction and with or without sub~titution by phenyl, or i8 a radical o~ the for~ula L-~X~XZ where L iB Cz-C~-alXylene and Xl and X2 are si~gly, ~ L ~1 tly o~ each other, C1-C5-alkyl or togethQr, together with the nitrogen atom joining them together, n 5- or C ~i Laturnted heterocyclic r~dical with or without an oxygen atom in the ring, and 3~
~5 i~ hydrogen, Cl-Cls-~kyl with or without lnterru~tion by ~rom 1 to 4 oxyqen atoms ln ether runction or a radical o~ the for~la L-N~lX2 where L, xl nd x2 are ~ach as de~in-d nbove, 4~
ns markcrs for L~d~o~ to a method for detecting these ben-2aldehyd-~ in hyll ~J~ c~ ~nd to hydrochrbon5 _ ~nq the ~ rrr~ }~r.~l 7.1r~ ,3 4~ US-A-5 145 573, VS-A-5 lB2 372 and EP-A-499 845 disclose azo dyes which are used as markers for minQral oil~ ~5-A-4 OC9 CC8 describes a method for mar~ang mineral oils ~ith disa20 dyes by OESRr1T SE I TE~ 2 ~ 21 9~0~ 9 V~ ~ hi 1; ~ nrj the dye added to the mineral oil by adding to the ~
rarked ~ineral oil an ad~LL~L which binds oth~r colored ingredien~s of ~he ~iner~l oil.
5 D~ 3 608 il5 and ~-A-3 724 757 describe benzopyran derivatives and their us- in r~cr~rr7;~g syster~.
Exs~ple 1 of D~-3-608 215 ~-- hQ~ the renction of 2,3-dimethyl-~L~ yllU~ tr~chlorozlncnt~ with 4-di~ethylr '-~b-nr~l~7~hyde 10 in ~ethanol to for the colored salt o~ tho formula ~ CE Ch ~ ~7(C~3)- ZnCl3~

W0-h-11 466~1994 d ~ hr.~ th~ use of substitut-d nnilines for marking ~in-rnl oils.
ZO
It is an object of thQ present invention to provide novel marker$
for l~ L~hv~ Tha novel markers rhould be readily ~h~t~;nnh30 ~nd ~oluble ln h~dL~r1LL~ ~bey should also be si~ple to de-tect; sp~ A3ly, even very Lmall nmounts of markc~r should bo 25 vi-ih;l17~h~e through a strong color renction.
We have ~ound that this object is nchleved by the above-defined h~n7~ld~hydes of the formula I.
30 Any ~lkyl or alkylene rpp~. ing in the nbo~~rLioned formula I
may be straig~t-chain or branch-d.
X1 and x2 co~bined with the nitrogen ato~ ~oini~g them togather into a 5- or C ~d s~Lu~L~d heterocyclic radical with or ~5 ~ithout an oxygen atom in the ring can be for cxn~ple pyrrol~di-nyl, p;r~ ;nyl or morpholinyl.
Rl, R2, R3, R4, R5, R6, X1 and X2 are each ior e~a~ple methyl, ethyl, propyl, isapropyl, b~tyl, isobutyl, ~ec-butyl, pentyl, ~0 isopen~yl, neopantyl, tort-pentyl, bexyl or 2-~ethylpentyl.
Rl, R2, R3, R4, R5 and R6 may eaah al~o be for ex~mple heptyl, oc~yl, 2-athylhexyl, f~coctyl, nonyl, isononyl, decyl, i~odecyl, undecyl, dodecyl, tridecyl, 3,5,5,7 teL. ylnonyl, isotri-45 decyl, t~Lad__~l or ~_~L~de~yl ~the above do~ignation~ isooctyl,i~30nonyl, 1sodecyl a~d isotridecyl are tr~vial name~ derived fro~
the oxo proce~s alcohol- - cf UllDann~s Encrclopedia of -~~ ~ - - - 2 I-~q 5 a ~ 9 Industri l Chemistry, 5th ~dition, Oo~ Al, p~ J~ ~u ~Y~
~l~o Vol A lQ, p~ge~ 2B4 and 2~5) Rl, RZ and R3 m y each ~l50 be $or exnmple methoxy, ethoAy, 5 pzopoxy, ;'~I~ butoAy, isobutoxy, L~c-b~to~y, p~ntyloxy, i~opentyloxy, neopentyloAy, tert-p-n~yloxy, hexyloAy, 2-~ethyl-pentylo~y~ heptyloxy, octyloxy, 2-ethylhexyloxy, i~ooctyloxy, nonyloxy, iso~onyloxy, decyloxy, isodecyloxy, UndecyloXy, dodecyloxy, tridecyloxy, 3,5,5,7-t~t, LLylnonyloxy, isot i-10 decyloxy, tuL -' ~loxy or ~cntadc_yloxy R~ ~nd R5 may ~ach also be for example 2 ' ~_Lhyl, 2-ethoYy-ethyl, 2-~ v~vA~_Lh~l, 2-ir ~ ~VA~_Lhyl~ 2-L~LOA~-~U~ 2- or 3 LLvAy~v~l~ 2- or 3 ~t~_y ~L V~ 1 ~ 2 or 3 ~ ~PVAY~V~11~ 2-15 or 3-L~L~A~lv~l, 2- or ~ - ~L~Lyl~ Z- or 4-~LLvA~b~Lyl~ 2-or 4-~ ~v~L~Lyl, 2- or 4-~Lv~yL~Lyl, 3,6 ~ ~ptyl, 3,6-vi-oxaoctyl, 4,8-dioxnnonyl, 3,7-dioxaoctyl, 3,7 ';~ ~nyl, 4,7-di-oxaoctyl, 4,7-dioxanonyl, 4,8-dioxadecyl, 3,6,8-~r~Yr~yl~
3,6,9-tr~ 1, 3,6,~,12-L~ L~ LLldecyl, ben~yl or 1- or 20 Z-phenyl-thyl ~ s for ex~mple (CH2)2, tcH2~3~ ~C~2)~, (cEz)s~ tCH2)C~ ~ch2) (C~2)8~ CH(C~)C~2 or CE( OE3~C~(CH3~
25 P _r~ according to the pr-~ent inv ntion is given to ~he u9e of b~n~ yd~s of the formula I where at least one of the radi-c~ls R~ to R3 i5 a radlc~l o~ the formula ~R4R5 Where R~ and R5 are each as de~ined above 30 Particular pre~erenc- for the marking o~ h~ L~ng is given to the ~e of ben~ ~hyde~ of the ~ormula Ia ~ 0 U: U~ (Ia), where Rl, R2, R~ and R5 are e~ch as deLined abo~e O partic~lar suitability are h~7Al~hyde5 of the ~ormula ~a where Rl and R~ nre 1rU_~ nt7y of e~ch other hydrogen, 45 hydroxyl, Cl-Cl5-~lkyl, Cl-Cl5-~lkoxy or a radical of the formula 21~ 9 S O ~ 51 CooR~ where R~ 1~ as de~lnea a~ove, ~- 5 L~ 15~ Y' and Rs i5 Cl-Cls-~lkyl.
P~rtlculrr pre~erenec for t~n m~rking o~ ~"5 i3 g~ven to 5 the use Or hr~ h~e~ of the form~lla Ia wh~re R4 and R5 ~re in-5 , ' tly Or each other Cl-Cl3-~lkyl and Rl and R2 are e~ch hydrogen Tne present inventio3 lso proTide~ a method of detect~ng ben-0 7~ das of form~la I in hy~ro~ , which ~ ~ r ~reat~ng the hydroc~bon w~th an ~_ al~lir or ~lroh~ medium g ~ protic ~cid, rt ieast one compound from the group o~
'~ conslstlns of ~ub~tltutad benzooyrylium 381t8 oS the formula II

- ~ ~ tII)~

where R7 is Cl-C8- ~Xyl, phcnyl, Cl-C5-alkoxy or haloge and R~ is r~thyl or R7 and R~ together are 1,4-butyleno and the ring ~ may be fused with a bonzene ring And may b- s~bstituted by C~-C~-alkyl, pyrrolidino, pi - A~, ~orpholino, chlorins or 25 bro~ine or in ring pc-it'on 7 ~~t~ lly also by hydroxyl, Cl ~~ rTy~ mono- or d~(C1-C5-alkyl~amlno which mly in turn be 8 bst~tut~d by chlorine or phenyl, and Xe is an option~ anion, and indoles Or the formula III

~ R9 ~III), where R9 and Rl~ are inA~ Ar~tly of each other hydrogen, hydrox-yl, a radical o~ the formula ~R4R5, ~here R~ and R5 are each as de~in~d abovo, Cl-C~-alkyl, phenyl, Cl-Cs-alkoxy or halogDn, nnd optionally a halide o~ th- m~tals zinc, alu~inu3 or tin P ~felenc~ ~ccording ~o thc present invention i8 g~ven to the ~se o~ indoles o~ the ~ormula III, s, '~lly 2-phenylindole ~5 _ ~ . 2~ 9Sa19 ~xamples o~ suitablo anions X3 are tetrachlorozinc~te, halide, sulfate, tetr fluorD~a~Q ~n~ phosph~te T_e ~r~n7~1 ~ohyde~ I, the benzopyrylium ~alt8 II ~nd also the ~n-5 doleL III are ~enerally known per se Marking for the purpo~e~ of the pre~ent invention is the ~ddition to h~d~v OlL~n~ of the ~ - l~hydes of the ~ormula I in ~uoh ~
C~ L~ On that, to the human eye, tb~ L~d~vcr~L~lL b~ve b~re-10 ly any or no vi~ble color, but the ~n~ e~ydes o~ the ~orml~laI A~e rnAdily and distinctly vi91hly detectable by the r~thods of Aotection ~ore p~ticuiarly ~ - ~~' her in ~he presen~ invention furth r provides hy~roe~r~n~ ¢o~prising 15 one or more of the 5 ~ hyd~s Or th- formula I
~IL~.G~Lo~s for th~ purpo~ea Or the present invention nre ~l~rhot~ or aromatic ~yd~ b~ which ure liguid undcr stan-dart condition~ ThQ~e are in ~rticular ml~eral oils, for exam-20 ple motor fuels, ~uch a~ gasolene, kQro~ene or diesel fuel, oroil~, ~uch a8 ~uQl oil or enginG oil ~he b~ A~hydes of the formula I are , Al ly ~uit~ble for marking mi~eral oils where 90~e ~orm of markinq is mandatory, for 25 ~ample for tax r~ason~ To keep the co~tg for t~is to a uinimu3, lt is de~ir~bl~ to keep th- a~ou~t of ~rrker uLed to a min~um To mark hydrocarbons, the b~ A~yd-~ of t e formul~ ~ are used either without a solvent or in thQ form of ~lut;~ Suit~ble 30 solvents Are organ~ c aolvents Pre~er~nce is given to u~ing ~ro-matic h~l~v -~ , 8uch a~ toluene, xyleDe, dodecylbenzono, di1sopropylnaphth~1ene or a mixtur~ o~ higher arom~tics ~vailable from Shell ~s 8hellsol0 AB ~o avoid tho rQculting 501ution h~ving ~ high visco~ity, the .~hc~L~LLon o~ hA-7-l~ohyde I
35 cho~-n for the olut;on gonQrally rrnge8 irom 5 to ~0 S by weight, based on t~o solution The ~olubility may bo improved by u~ing ~urther, co-solventi, for examplQ ~lcohols, 8uch aJ me~hanol, ethA~ol, propa~ol, ~Aprop~n-40 ol, butanol, isobutanol, pentanol, hexanol, heptanol, octanol,2-6thyl~ex~301 or cy~lAhovAnAl~ glycol6, such as butylethyle~e ~lycol or methylprcpylene glycol, zmine8, such as triethylamine, dL1800ctylamine, dLcyclohexylamLne, aniline, ~-methyla~ ne, ~,~-dimethyla~iline, to~ 1ne or xylidine, ~ uoh 45 as 3-~2-methoxyethoxy)propylamine, o-cresol, m-cresol or p-cre501, ketone~, ~uch a~ diethyl keto~e or cy~1 ~h~v=n~n~
1 w tam~, such ~s y-butyrolactone, carbonates, ~uch a~ othylene ~C01~1T ~ T Tn~l R':/

- 2~ ~501 9 : 6 c-rbonate or propyl-~e rA hnnn1~ pheno}s, LU -h a9 t~DUtylp~enol cr no~ ~nol, esters, such as methyl phthalate, ethyl ~hth~late, 2-ethylheXyl phth~l~te, ethyl acetate, butyi acet~te or cyclohexyl acetate, ~mid-s, ~uch as N,~-di~ethylfr~r-~;~~, ~,N-diethylo~ or N-methylpys~ ~, or mixtures thereof.
~h~ h~n7-l~hyd~s of the formul~ I to bQ u5Qd o~crr~in~ to the pre~ent ~nvantlon perm~t very simple detection o~ marked hydro-10 carbons, ~ven i~ th m~rker substancec are prc~ent only in a con-centration o~ ~bout 1~ ppm or les~.
~he presence in l~d~ h~ of the _ ~ o~ the formula I
u~e~ as m rkers i~ ~d.~ ly detected on treating the hydro-15 carbon with an a~ alrnhnlic or ~ nl;~ medium ~ ng apyryllum salt o~ th~ formula II and/or an indol- Or the ~ormula III, u protio aeid and optionally a h-lid- o~ the metals z~nc, ~ ~ or tin. In aqueou~-Alrnh~l~c media, the Weight ratlo of w~t r : Alcohol varies from 0.5 : 1 to 4 : 1, and is preferably lQ ~bout 1 : 1. The ~es~lt is a di~tinctly ~i~ible color change Or th- -_~D Alrnhr~ ph~se.
Suitable al cohols lnclud- for ex~mple ethanol, propanol, iso-propanol, l-meth~ 2-ol, ethylene glycol or 1,2- or Z~ 1,3-propylene glycol. Tho use o~ ethanol is ~ ~L~r~d.
Suitabl- protlc ~cids for the method oi the present invention in-clude in particular strong acids, i.e. protic acids who~e pX_ v~lue i~ e 3.5 Such acids include for examp}e i~rg-~r or 30 organlc ncid~, ~uch _s perchlor~c acld, hydroiodic acid, hydrochloric acid, hln ~ ' r acid, hydro~luoric acid, ~ulfuric ecld, nitria acid, ~ acid, ~ ~ ~ lf~n;r acid, toluene3ul~0nic acid, naphth-l r- 1 fr-i r acid~ ~n U1 ~rn ~ ~
ncid, oxalic acid, maleic aoid, chl~l~r- ~c acid, dichloroacetic 35 aeid or bromoacetla acid. In some cases it can be of advantage to ~uf~er these _cidL, for e~ample by ~dding acetic acid.
-~s ~ell as to o- or p-tolum~E lrOn;~ acid, ~L.~eL~ is given ~speclally to inorganic acids, with hydrochlorio acid and sul~u-4~ ric acid being particularly p ef~l~ ~d.
suit-ble halides o~ the metals zinc, Al--~ or tin include for ~ ~mple zinc chlorid , zinc bromide, aluminu~ chloride, aluminu~
bromide or t~n ~etr~hl ~r~ *~ 7inc ~hl ~r; ~ p rticularly pre-45 ~erred.

21 ~ 9 ~t is genorally s~ff;~ont to ex~ract rro~ about lo to ~o ~ or - - -tbe h~d~colL~ ~arked according to the present inventlon with f~om 1 to 50 ~1 o~ an aUu~u~~ A~Al;r or ~7~A~t~r so~ut~on o~
a pyryliu2 salt of the ~ormula II and~or of an indole oi the for-muia III, a prot~c acid, nrt~An~l7y in tho pre~ence of ~ ~etal halide, to obtain a color change It ic ~tso po~iblo to r~place th~ Jolution Or th- protic aeld by An ~ Ahnl~ solution of a 2etal halide ~lone, sincY the latter likewise has an acid roaction lC
Th~ ~oaca~LL~Oion o~ th~ protio acid ln tho -_ &7 ~AhAl; ~ or AhA~ olution is ~enorally from 5 to 50 ~ by weiqht, pre~er-~bly ~rom 10 to 30 ~ by w ight The ccnc~uLLOLlon of met~l halide ~s generally from O to 50 % by weight, pre~erably fro~ 5 to 20 1~ by w~ight, in each case ba3ed on the wQlght Or thQ solution .
On- considerabl- __ o~ the inventlon is that two different r~thods can be us-d ~or ~te~t; ng the L ~7~yde~ o_ the rOr-mula I Detect~on i~ ~Ic Gf~ vQry r-liable, even in the pres-ZO ence of pos~ible int~f~ce teg additives in diesel ~uel) The Examples which fol_ow illustrate the in~ention Gener~7 method 1 Co~mercial diesel _uel wac mix-d with 10 ppm each o~ benzaLde-hyde ~or this the aldehyde was prediccclved in toluena ~n 0 1 ~trength by wei~ht and this solution w~5 added to the diesel ~u~l .
In each of ~xamples 1 to 12 10 ml o~ the diesel fuel thus ~rked were admixcd with 2 ~1 of reagent solutlon and shaken for 5 min-utes Then 1 m~ of water was added ~nd the shaking was continued for a further 5 minute~ Tho aqueou~ phase showed the color ln~i-3~ catod below in T~ble ~o ~QagQ~t solution 1 5 ~i of 1 % Ltrength by weight indole i ethanol 40 5 21 Or ~ ~ ~ LL~L~d hydrochloric acid 5 g of zinc chloride 95 21 0~ acetic acid 4 i ~ 21 9~0~ 9 ... .... ~ ~ -Reagent ~olution 2 ~ ~
... . ~
S ~1 o~ 1 ~ trength ~y welght 2-methylindole in c~hannl 5 ml 0~ C~e~LL aLed hydrochloric ncid 5 g o~ zinc chloride 95 rl o~ acstic acid R~agant solution 3 lD S ~1 o~ 1 ~ strength by weight 2-phenylindole in ethanol 5 r~ of L~C~.~ ~d hydrochloric acid ~5 g Or zino chloride 95 ml o~ ace-~c acid 15 P rticularly advantageouc re~ults are o~taincd cn rir~t f~lteri~g the die-cl fuel through cillca gel.

3~

Table No. 1 ~ ' ~~-- ~ ' -~~ /-E~c. No. Aldehyde Roagont Color - 5 1 1 mz~g~:ntn ~3~
~?( C}~3 ) z 2 2 v$olet c:~O

N~ 3 ) z 3 :~ Yiolet ceo ~3 N~C~13)z 4 1 orange CEIO

~3~o3 ~ C2~;~ ) z 2 reddish viole~
C~O
~ - ~o~
~o b~

~(czEs~z .~

--~ r ~ =
21 9 5 (~1 9 I!:X. I~o.~ldehydo ~e~gent Color 6 3 ~gent~
C}~O
~3~~~

l~lr2~s~
0 ~ c}~o 1 orange 0E~

~_ 8 CEO 2 reddi~h violet g CEO 3 2D.~Lgent~

~OE

3~ o~
1 r-ddi~h violclt CHO
~C02CH3 N(CH3~2 Ex. ~o. Alduhyd- Ru~qent Color 11 2 blulsh ~iolet a~o ~COzC1~3 3 ) z lD 12 3 blui~h violet ~0 ,~COzC}i~

~S
N(C~3)2 81~il~r result~ are DbtAIned o~ u9ing marker~ ;"g the ~ ~hyde~ l~sted below 1~ T~ble ~o. 2.

T~le No. 2 Ex. ~o. Aldehyde 25 ~3 C~o ~3 N~C2~s)z CEIO

~lC82CCE15) z ~0 - -- ~ 2195019 Ex. 1~ ehyd~
1 5 CE~0 [~3 1 6 Cl~0 ~ ~3 2 CE!3-N-c2~l4c;
l B c}10 0~1 ~C~3)2 19 C~O
3s ~3~~~
( ( c~2c6El5 ~ 2 ~1 ,. OCEI3 W

N(C2E~s)2 _ .

-- s - 13 219$0f9 Ge~rnl mcShcd 2 Cor~rcial die~el fuel wa~ xed with 10 pp~ o~ each benz~lde-hyde. For this the ~ wa8 p~edi~ol~-d ln teluune ~n 5 0.~ ~ ~trength ~y weight And th~J solutlon WR~ ndded to th- die-~1 fuel.
In e~ch of Exnmples 21 to 30 10 ml of the m2rked die~cl fu-l wer-~ixed with 2 ml of re~gent solution 4 And refluxed ~or 5 ~n-10 ute~. Then 1 ml of 1~1 vtv water~eth~nol w~n ncded And the mi~-tur~ wan shaXen for 5 m~nut-3s. The aquecu~ ph~e shAowed the color ~n~r~tD~ ~elow {n Table No. 3.

~eagent Lolution 4 5 ml of the ~ zo~l~ylLul~ ~alt of the for~ula ~ Q~3 ZnCl 1 ~ ~trength in w~ter 25 ml o~ atLd hydrochloric acid - 22~ ml of acetic ~cld T~ble 3 EX. No.Aldehyde Q CDlor 21 C6~5 ~lue C~O

3~ [ ~

NtCEI3)z ,0 22 C~3 ~lu~
CEIO

~(C~S3 ) il - ~ ~ 219501 9 Ex. No. ~ldehyde Q Color 23 Cc~is blue CE~O
S ~ ~2CEI3 N~CEi~)2 10 24 ~ blue C~O
~ CO2CII3 N~CE~3~2 Z5 cH3 bluo C~IO

~' ~t C~5 ) 2 26 C~iO C~l~ blue o~
~3~

35 27 CEI0 ~ blue ~~~~~

O~

4~ .

; ~ ' 2i 9501 9 '' 15 Ex. ~o. ~ldehyde Q Color 28 C~3 red~ish violet C~O

0~

10 2~ c~3 reddi~h violet C~o ~ 1 OC~3 C~3 violet C~O
~ OC~

Similar results are obt ~ned on repl~cing the benzopyrylium salt o~ reagent col~tion 4 ~y that Or the formul~

1~0 Z~C13e g5

Claims (5)

We claim:

1. The use of benzaldehydes of the formula I

in which the ring A may be benzofused, and R1, R2 and R3 are each, independently of one another, hydrogen, hydroxyl, C1-C15-alkyl, C1-C15-alkoxy,cyano, nitro or a radical of the formula NR4R5 or COOR6 where R4 is hydrogen or C1-C15-alkyl with or without interruption by from 1 to 4 oxygen atoms in ether function and with or without substitution by phenyl, R5 is C1-C15-alkyl with or without interruption by from 1 to 4 oxygen atoms in ether function and with or without situation by phenyl, or is a radical of the formula L-NX1X2 where L is C2-C8-alkylene and X1 and X2 are singly, independently of each other, C1-C6-alkyl or together, together with the nitrogen atom joining them together, a 5- or 6-membered saturated heterocyclic radical with or without an oxygen atom in the ring, and R6 is hydrogen, C1-C15-alkyl with or without interruption by from 1 to 4 oxygen atoms in ether function or a radical of the formula L-NX1X2 where L, X1 and X2 are each as defined above, as markers for hydrocarbons.

2. A use as claimed in claim 1 wherefor the benzaldehydes conform to the formula Ia where R1, R2, R4, and R5 are each as defined in claim 1.

3. A use as claimed in claim 1 or 2 wherefor R1 and R2 are independently of each other hydrogen, hydroxyl, C1-C15-alkyl, C1-C15-alkoxy or a radical of the formula COOR6 where R6 is as defined in claim 1, R4 is hydrogen or C1-C15-alkyl and R5 is C1-C15-alkyl.

4. A method of detaching benzaldehydes of formula I as set forth in claim 1 in hydrocarbons, which comprises treating the hydrocarbon with aqueous-alcoholic or alcoholic medium comprising a protic acid, at least one compound from the group of compounds consisting of substitute pyrylium salts of the formula II

where R7 is C1-C8-alkyl, phenyl, C1-C5-alkoxy or halogen and R8 is methyl or R7 and R8 together are 1,4-butylene and the ring B may be fused with a benzene ring and may be substituted by C1-C4-alkyl, pyrrolidino, piperidino, morpholino, chlorine or bromine or in ring position 7 optionally by hydroxyl, C1-C4-alkoxy, mono- or di(C1-C5-alkyl)amino which may in turn be substituted by chlorine or phenyl,and X.THETA. is an optional anion, and indoles of the formula III

, where R9 and R10 are independently of each other hydrogen, hydroxyl, a radical of the formula NR4R5, where R4 and R5 are each as defined in claim 1, C1-C8-alkyl, phenyl, C1-C5-alkoxy or halogen, and optionally a halide of the metals zinc,aluminum or tin.

5. A hydrocarbon with a marker comprising one or more benzaldehyde of the formula I as set forth in claim 1.