United States Patent O Fice Patented Dec
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2,816,144 United States Patent O fice Patented Dec. 10, 1957 2. conventional manner and the hydrolysis mass is heated until completely free of any side chain chlorine deriva 2,816,144 tives. This can be determined by the use of alcoholic silver nitrate, for example, which will form a cloudy pre PROBEDUCTION OF RBENZALDEHYDE cipitate upon contact with compounds containing a side Robert W. Harris, Silsborough Township, Somerset chain chlorine group. County, N. S. The benzaldehyde which is obtained upon hydrolysis Separates from the aqueous layer and upon washing and No Drawing. Application August 4, 1955, fractionating yields a substantially pure compound which Seria No. 526,574. 0 is totally free from chlorine. 8 Claims. (C. 260-599) The chlorination of toluene is essentially a step-wise reaction and thus the chlorination can be terminated be fore more than two or three percent is converted to the The present invention relates to a process for the pro 5 tri-chloro derivative. This will correspond to a benzal duction of benzaldehyde from toluene. More particu chloride content of no more than about 35%, depending larly, it relates to a process wherein toluene is reacted upon the particular conditions of the reaction, the balance with chlorine and hydrolyzed to produce benzaldehyde being benzyl chloride with a minor amount of unreacted free from chlorine. toluene. Consequently, the reaction is terminated far The chlorination of toluene will result in the introduc 20 short of the maximum formation of benzal chloride so tion of one, two or three chlorine atoms in the methyl that substantially none of the toluene is lost through the side chain. The alpha-mono-chloro-toluene (benzyl chlo formation of the tri-chloro derivative. In spite of the fact ride) upon hydrolysis will yield benzyl alcohol, the benzal that only about one-third of the toluene is converted to chloride will yield benzaldehyde, and the benzotrichloride the desired material the process is economical in that the upon hydrolysis will produce benzoic acid. Accordingly, balance of the materials may be recycled while substan in the preparation of benzaldehyde from toluene by chlo tially none of the less valuable benzoic acid is formed. rination, it is desirable that only a limited amount of The toluene should be dry, of high grade suitable for benzotrichloride is formed. side chain chlorination and substantially pure, i. e., free Heretofore in the preparation of benzaldehyde, toluene from Sulphur compounds, paraffins, etc. Nitration grade has been chlorinated to a mixture of the di-chloro and 30 toluene is a suitable starting material. The chlorination tri-chloro derivatives in the approximate ratio of about is effected in the liquid phase with dry chlorine which 4 to 1 or higher. The chlorination product was run into may be bubbled into the toluene. Ultra-violet light, pos a slurry of calcium carbonate in water to thereby convert sibly with the addition of other materials usch as phos the di-chloro derivative to benzaldehyde and the tri-chloro phorus trichloride, may be used to catalyze the reaction derivative to calcium benzoate, the benzaldehyde being 35 although preferably no such additions are employed. The steam distilled and the calcium benzoate being acidified reaction is preferably conducted at the boiling point of to form benzoic acid. An alternate method of effecting the toluene with moderate reflux and under all circum the hydrolysis was to employ the use of sulphuric acid or stances the use of metal containing catalysts or equipment water to form benzaldehyde and benzoic acid. is avoided since they catalyze ring chlorination of the In all of these procedures, however, an appreciable 40 toluene. In producing benzaldehyde which is free from quantity of the toluene was ultimately converted to benzoic chlorine, it is essential that such ring chlorination be acid rather than benzaldehyde because of the high degree avoided since several of the possible ring chlorinated of chlorination. In addition, both the benzaldehyde and compounds will boil at a temperature so close to the boil benzoic acid fractions are more or less contaminated with ing point of benzaldehyde that they cannot economically derivatives containing chlorine in the benzene ring. 45 be separated by distillation. Accordingly, plastic or glass It is accordingly an object of the present invention to reaction vessels are employed. provide a process for the preparation of benzaldehyde In conducting the chlorination, when about 10% of from toluene by chlorination and subsequent hydrolysis the toluene has been converted to the di-chloro derivative wherein but little of the toluene is converted into benzoic there will be about 45% of mono-chloro derivative, the acid. 50 balance being unreacted toluene. When 35% of the toluene has been converted to the di-chloro derivative It is a further object of the present invention to provide there will be about 55% to about 65% of the mono a process for the preparation of benzaldehyde which is chloro derivative. Possibly 2 to 3% of the tri-chloro de free from nuclear or side chain chlorine. rivative may be present. As the proportion of the di Another object of the invention is to provide a process chloro derivative increases the proportion of the tri-chloro for the chlorination of toluene wherein benzal chloride 55 derivative will likewise increase and it is thus desirable is formed to an appreciable extent while avoiding the that chlorination be terminated when as large an amount formation of benzotrichloride as well as ring chlorinated of benzal chloride has been formed without formation of derivatives of toluene. any appreciable amount of the tri-chloro derivative. Ac It has now been found that if toluene is chlorinated cordingly, the chlorination is generally terminated when until no more than about 35% has been converted to 60 about 5% to 35% and preferably 10% to 30% of the benzal chloride substantially none of the toluene will have toluene has been converted to benzal chloride. been converted to the tri-chloro derivative. Upon dis In effecting the distillation the unreacted toluene may tillation of the reaction mixture any unreacted toluene be removed at reduced pressures. Upon increasing the will first boil off followed by the benzyl chloride. The vacuum to about 1 to 10 mm. the benzyl chloride can final fraction will contain benzal chloride possibly admixed be boiled off leaving the desired benzal chloride. This with a small amount of the tri-chloro derivative. latter is preferably redistilled at a pressure of about 1 or The unreacted toluene and benzyl chloride may be re 10 mm. to yield substantially pure benzal chloride free cycled for further chlorination while the benzal chloride from nuclear chlorine atoms. The hydrolysis may be fraction is preferably redistilled to yield benzal chloride effected with aqueous Sulphuric acid, steam plus zinc coin of 97 to 98% purity. 70 pounds, or water. The benzaldehyde separates from The benzal chloride is hydrolyzed to benzaldehyde in the aqueous layer and is preferably neutralized or washed 2,816,144 3. 4 with alkali such as dilute soda ash prior to being frac 155 and 420. Column drain back and residue amounted tionated. A distillate is obtained free from nuclear and to 90 grams. side chain chlorine atoms. The benzal chloride cut of 420 grams was refractionated The following examples, illustrate several, processes through a small high efficiency column to yield 390 grams. which have been found suitable in the practice of the in- 5 Here the vacuum was accurately regulated at 5 mm. and the pure cut taken at a constant temperature. Upon vention: hydrolysis this yielded 252 grams of benzaldehyde. Example I Fractionation of the latter yielded 240 grams of ben One liters (approximately 865 grams) of freshly dis Zaldehyde free from chlorine. tilled nitration grade toluene was placed in a two liter O Various changes and modifications may be made with glass flask equipped with a high speed agitator, a gas inlet, out departing from the spirit and scope of the present reflux condenser and a quartz U. V. lamp. Heat was . invention and it is intended that such obvious changes applied until toluene was refluxing and dried chlorine gas . and modifications be embraced by the annexed claims. run in, slowly at first and gradually increased as the reac I claim: tion proceeded. The flow was set at a maximum per 1. The process, which comprises reacting toluene with mitted by the capacity of the condenser, but at all times chlorine while avoiding contact with metals until no held beneath the point at which any free chlorine passed more than about 35% of the toluene has been converted through the liquid. to benzal chloride, distilling the reaction mass to separate After twelve hours flow of gas and periodically there the benzal chloride, and hydrolyzing the benzal chloride. after, samples were drawn and tested for specific gravity. 20 to benzaldehyde. When the gravity read about 1.16 at room temperature, 2. The process which comprises reacting substantially the gas was cut off and the slightly yellowish liquid al pure toluene with dry chlorine at elevated temperature lowed to cool while exposed to the U. V. light until . while avoiding contact with metals until about 5 to about colorless. 35% of the toluene has been converted to benzal chloride . The resultant mixture weighing 1267grams and analyz . at which point substantially, none. of the toluene has been ing by weight approximately 1.0% toluene, 63.0% benzyl converted to benzotrichloride, distilling the reaction mass chloride, 33.0% benzal chloride, 2% benzotrichloride, to separate. the benzal chloride, and hydrolyzing the and 1% nuclear chlorinated bodies, was transferred to a . benzal chloride to thereby obtain benzaldehyde substan one liter still equipped with a column having a twenty tially free: from nuclear and side chain chlorinated com plate equivalent, a thermometer at the top, reflux and .30 pounds.