United States Patent Off 3,322,833 Patented May 30, 1967 2 3,322,833 from the group consisting of halogen, nitro and hydrogen. PREPARATHON OF ARMATIC ALDESYDES Examples of specific compounds include: Edward J. McNeis, Wallingford, Pa., assignor to Sun benzyl alcohol 9. Conpany, Philadelphia, Pa., a corporation of New o-methyl benzyl alcohol ersey 5 m-methyl benzyl alcohol No Drawing. Filed Jan. 24, 1963, Ser. No. 253,764 p-methyl benzyl alcohol A1 Claims. (C. 260-599) m-isopropyl benzyl alcohol This invention relates to aromatic aldehydes and more p-isopropyl benzyl alcohol particularly to a method for preparing such aldehydes p-t-butyl benzyl alcohol by oxidation of the corresponding aromatic alcohols in 0. p-n-amyl benzyl alcohol accordance with the following reaction: m-neohexyl benzyl alcohol m-n-heptyl benzyl alcohol X X p-diisobutylbenzyl alcohol m-(2-methyl octyl) benzyl alcohol PbO 15 p-n-undecyl benzyl alcohol R CHOF - R1 CHO p-(2-methyl-5-ethyl-7,7-dimethylnonyl) benzyl alcohol p-(2,4,6,8-tetramethyl undecyl) benzyl alcohol R R 2,6-dimethyl benzyl alcohol wherein R1 and R2 are selected from the group consisting 20 3,5-diethyl benzyl alcohol of hydrogen, an alkyl radical containing from 1 to 18 3-ethyl-5-t-butylbenzyl alcohol carbon atoms, and an alkoxy radical containing from 1 2-methyl-4-neopentyl benzyl alcohol to 18 carbon atoms, and X is a nuclear substituent 3,5-di-n-dodecyl benzyl alcohol Selected from the group consisting of halogen, nitro, and 2,6-dimethoxy benzyl alcohol hydrogen. 25 3,5-diethoxybenzyl alcohol Aromatic aldehydes are used extensively in the syn 2-methoxy-4-butoxy benzyl alcohol thesis of other organic compounds. Other specific uses p-nitro benzyl alcohol m-chloro benzyl alcohol forand aromaticsynthetic aldehydesperfumes. include those of flavoring agents p-bromo benzyl alcohol. A number of methods have been disclosed in the prior 30 2-methyl-4-nitro benzyl alcohol art for the preparation of aromatic aldehydes. They in 3-methoxyl-5-chlorobenzyl alcohol clude hydrolysis of dihalides, Gattermann's carbon mon 2,6-dimethyl-4-nitro benzyl alcohol oxide synthesis using formyl chloride or the equivalent 2,6-diethyl-4-bromo benzyl alcohol thereof, and oxidation of various aromatic materials. The aromatic alcohol can be contacted with the lead Aromatic compounds having either alkyl substituents or 35 dioxide either in the presence or absence of a solvent hydroxy substituents are highly susceptible to oxidation. material and in an inert atmosphere. It is preferred that It has been found that unless extremely carefully con prior to contacting the aromatic alcohol with lead dioxide, trolled conditions be used, the oxidation of such com it be dissolved in a suitable solvent. It is important that pounds leads to the formation of aromatic acids rather the solvent be inert and not be susceptible to oxidation. than aromatic aldehydes. In order to prepare aromatic 40 Examples of suitable solvents include chloroform, ben aldehydes by oxidizing an aromatic material such as tolu zene, nitrobenzene, chlorobenzene, diethyl ether, and pe ene, it has been found necessary to conduct the oxidation troleum ether. Petroleum ether and diethyl ether are the in the presence of a material such as acetic anhydride preferred solvents. which would effectively react with the aldehyde group as As stated above the oxidation reaction is carried out it is formed and thus prevent the further oxidation there 45 in an inert atmosphere. Examples thereof include nitro of to the corresponding aromatic acid. The effect of such gen, methane, and carbon dioxide. Nitrogen is the pre blocking reaction necessitates Subsequent processing steps ferred material. such as hydrolysis to recover the desired aldehyde The temperature at which the aromatic alcohol or product. solution of aromatic alcohol is contacted with the lead A method has now been found whereby aromatic alde 50 dioxide can vary over a wide range. It has been found hydes can be prepared directly from the corresponding that substantial amounts of aromatic aldehyde products aromatic alcohols without the need for any blocking re are produced at a temperature of 20° C. or lower. If the action to take place. - aromatic alcohol is not contained in a solvent, the maxi Briefly the instant invention comprises contacting an mum temperature to which the reaction mass can be aromatic alcohol, such as benzyl alcohol, with lead di 55 heated is goverened only by the decomposition temper oxide at a temperature in the range of 0° C. to 250 C. ature of the aromatic alcohol. If the alcohol is dissolved in an inert atmosphere for a period of time ranging be in a solvent prior to the contacting thereof with the lead tween 10 seconds and 50 hours and recovering an aro dioxide, the maximum temperature to which the reaction matic aldehyde product. Suitable aromatic alcohols which mass can be heated is governed by the boiling point of the can be used to prepare aromatic aldehydes in accordance 60 solvent at the pressure used. While temperatures rang with the instant invention have the general formula ing betwen 0°C. to as high as 250 C. can be used in this invention, it is preferred that a temperature ranging be tween about 20 C. and 100 C. be used. 65 The time that the reaction mixture is contacted can R CHOH vary between 10 seconds and 50 hours or longer. It is preferred that the contacting time range between 0.5 R hour and 24 hours. wherein R1 and R2 are selected from the group consisting The molar ratio of lead dioxide to the aromatic alcohol 70 can also vary over wide limits. It has been found that if of hydrogen, alkyl radicals containing from 1 to 18 car trace amounts of lead dioxide are present in the reaction bon atoms and alkoxy radicals containing from 1 to 18 mass, there is produced some aldehyde product. It is pre carbon atoms, and X is a nuclear substituent selected ferred, however, that the molar ratio of lead dioxide to 3,322,833 3. 4 18 carbon atoms, and X is a nuclear substituent selected alcohol be in the range of from about 1:100 to 100:1 from the group consisting of halogen, nitro and hydro with a molar ratio ranging between about 3:1 and 10:1 gen, contacting the resulting solution with lead dioxide being most preferred. at a temperature in the range of from 0° C. to 250 C. for Since the instant process involves a heterogenous re a period of time ranging between 10 seconds and 50 hours action system, the recovery of the desired aldehyde prod in an inert atmosphere and thereafter recovering said uct is effected by first separating the solid lead dioxide aromatic aldehyde product. from the liquid phase by conventional methods such as fil 4. Method in accordance with claim 3 wherein said tration. The filtrate containing aldehyde and unreacted solvent is selected from the group consisting of chloro alcohol is subjected to fractional distillation. The alde form, benzene, nitrobenzene, chlorobenzene, ethyl ether, hyde is recovered therefrom and the unreacted alcohol 0. and petroleum ether. and solvent can also be recovered and recycled. 5. Method in accordance with claim 4 wherein the The following example further illustrates the instant temperature is in the range of from 20° C. to 100 C. invention. and the period of time is from 0.5 hour to 24 hours. Example 5 6. Method in accordance with claim 3 wherein the A solution of 0.4062 g. benzyl alcohol dissolved in 50 temperature is in the range of from 20 C, to 100° C. and ml. of ethyl ether was contacted with 23.9 g, of lead di the period of time is from 0.5 hour to 24 hours. oxide for 18 hours at room temperature (20° C.) in a 7. Method for preparing aromatic aldehydes which nitrogen atmosphere. At the end of the reaction time comprises dissolving in an inert solvent an aromatic the mixture was separated by filtration. Upon infrared 20 alcohol having the general formula analysis and vapor phase chromotography, the ether fil trate was shown to contain 50% by weight benzaldehyde and 50% by weight unreacted benzyl alcohol. The yield of benzaldehyde was 55%. R CHOEI Substantially similar results are obtained when other of 25 the solvents named above are substituted for ethyl ether R and when other aromatic alcohols such as p-methylbenzyl wherein R1 and R2 are selected from the group consisting alcohol, p-t-butyl benzyl alcohol, 2-6-dimethyl benzyl al of hydrogen, alkyl radicals containing from 1 to 18 carbon cohol, 2,6-dimethoxybenzyl alcohol, p-nitro benzyl alco atoms and alkoxy radicals containing from 1 to 18 carbon hol, and p-bromobenzyl alcohol are substituted in the 30 atoms, and X is a nuclear substituent selected from the foregoing example. group consisting of halogen, nitro and hydrogen, con I claim: tacting the resulting solution with from 0.01 to 100.0 1. Method for preparing aromatic aldehydes having moles of lead dioxide per mole of alcohol starting material the general formula at a temperature in the range of from 0° C. to 250° C. for a period of time ranging between 10 seconds and 50 hours in an inert atmosphere and thereafter recovering R CEO said aromatic aldehyde product. 8. Method in accordance with claim 7 wherein the 40 molar ratio of lead dioxide to alcohol starting material R is in the range of 3:1 to 10:1. wherein R and R2 are selected from the group consist 9.