[CONTRIBUTION FROM THEINSTITUTE
OF PAPER CHEMISTFCY]
SILVER CATALYZED REACTIONS OF PHENOLIC ALDEHYDES1 IRWIN A. PEARL
Received J u l y 29, 1946
In previous papers the quantitative oxidation of vanillin t o vanillic acid with alkali and one-half mole of silver oxide (1, 2) and the Cannizzaro reaction of vanillin in the presence of metallic silver (3) were reported. In order to determine whether these reactions were characteristic of vanillin alone or could be applied to other aldehydes which fail to undergo the Cannizzaro reaction under ordinary conditions (4),the study reported herein was initiated (5). This paper presents a number of experiments on other o-and p-hydroxybenzaldehydes. The compounds studied were o-vanillin, 5-chlorovanillin, salicylaldehyde, and p-hydroxybenzaldehyde. In addition p-dimethylaminobenzaldehyde,which heretofore could not be made to undergo the Cannizzaro reaction (6, 7), was investigated. Reaction of o-vanillin (2-hydroxy-3-methoxybenzaldehyde)with 0.5 mole of silver oxide and excess alkali gave an almost quantitative yield of 0-vanillic acid. Like its p-analog, o-vanillin had never been oxidized in good yield directly to o-vanillic acid. Rupp and Linck (8) succeeded in obtaining high yields of o-vanillic acid from 0-vanillin by heating with potassium hydroxide a t 215". 5-Chlorovanillin was easily oxidized with alkali and 0.5 mole of silver oxide to the corresponding acid. When the silver oxide-vanillin ratio was reduced further, 5-chlorovanillyl alcohol appeared in the theoretical amount calculated on the basis of a Cannizzaro reaction (1). Reaction of 5-chlorovanillin with alkali in the presence of active silver metal gave equivalent amounts of acid and alcohol, and the crossed Cannizzaro reaction of 5-chlorovanillin with formaldehyde in the presence of active silver yielded only 5-chlorovanillyl alcohol. Salicylaldehyde acted in exactly the same manner as did 5-chlorovanillin. In all Cannizzaro experiments with these two aldehydes, the alcohols were isolated in their uncondensed state, thus acting differently from vanillyl alcohol under the same conditions (1, 3). p-Hydroxybenzaldehydewas easily oxidized with alkali and 0.5 mole of silver oxide to p-hydroxybenzoic acid, and readily underwent the regular and crossed Cannizzaro reactions in the presence of active silver. In the latter reactions, acidification of the filtered reaction mixtures with strong acids yielded p-hydroxybenzyl alcohol in a polycondensed form, but acidification with a weak acid, such as carbon dioxide, gave the uncondensed p-hydroxybenzyl alcohol. Analogous reactions of vanillin gave the polycondensed alcohol under all aciacation conditions, except in the presence of a large excess of formaldehyde (1,3). 1. This paper represents a portion of the results obtained in the research program sponsored by the Sulphite Pulp Manufacturers' Committee on Waste Disposal and conducted for the Committee by The Institute of Paper Chemistry. Acknowledgment is made by the Inst,itute for permission on the pert of the Committee to publish these results.
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IRWIN A. PEARL
Dismutation of p-dimethylaminobenzaldehyde by means of the Cannizzaro reaction took place with ease in the presence of active silver to yield equivalent amounts of p-dimethylaminobenzoic acid and p-dimethylaminobenzyl alcohol. This was the only aminobenzaldehyde studied, but the results obtained indicate that active metallic silver will probably catalyze the Cannizzaro reaction of all o- and p-hydroxy, amino, and substituted aminobenzaldehydes which are unaffected by alkali alone. In the above experiments, if the active silver used was prepared by reduction with the aldehyde of silver oxide prepared in situ from alkali and silver nitrate (Process II), the yields of the acid in the Cannizzaro reactions were alxays greater than 50%. This is more evidence that some of the active silver metal produced in the aldehyde oxidation reaction is reoxidized to silver oxide by the nitrates present in the reaction mixture. Reuse of the active silver a h a y s gave equivalent amounts of acid and alcohol. The oxidation of aldehydes ordinarily not amenable to the Cannizzaro reaction, by means of alkali and 0.5 mole of silver oxide, affords a simple laboratory method for the preparation of the corresponding acids. This is especially true in those instances in which the aldehyde is readily available, e.g., vanillin and o-vanillin. All the above reactions employing catalytic silver were repeated without the use of silver and in none of the latter cases did reaction take place, the aldehyde being recovered in all instances. EXPERIMENTAL
All melting points given are uncorrected. Xtarting materials. o-Vanillin (2-hydroxy-3-methoxybenzaldehyde)was a commercial technical product furnished by Monsanto Chemical Company. It was used without further purification. 5-Chlorovanillin was prepared by the method of Menke and Bentley (9) and was obtained as white crystals melting a t 164-165". The other aldehydes used were Eastman Kodak Company products and were used without further purification. T o avoid repetition, details have been given for representative reactions. Analogous reactions discussed above and given in Table I were carried out by the following methods with slight variations required in individual cases. Reaction of o-vanillin with alkali and 0.6 mole of silver oxide (Process I ) . Silver oxide was freshly prepared by mixing 25% solutions of 307 g. (1.8 moles) of silver nitrate and 75 g. (1.8 moles) of sodium hydroxide, allowing to settle, and decanting the supernatant liquor. The oxide was filtered, washed well with water, transferred to a 6-liter beaker, and covered with 3000 cc. of water. With vigorous stirring the silver oxide suspension was treated with 362 g. (9 moles) of sodium hydroxide. The temperature at this point was 40". With continued stirring 275 g. (1.8 moles) of o-vanillin was added at one time. A very vigorous reaction set in and the temperature rose to 80". Stirring was continued until the temperature dropped to 50°, and then the reactionmixture was allowed to settle. The fluffy precipitated silver was filtered and washed with water. The combined filtrate and washings were acidified with dilute sulfuric acid and cooled. The white crystals which separated were filtered, washed with water, and dried; the yield was 269 g. (89.1%) of o-vanillic acid melting at 150-152'. Extraction of the filtrate with ether yielded an additional 13.3 g. (4.4%) of ovanillic acid as a white solid which was recrystallized from water t o give n-hite crystals melting at 151-152'.
REACTIONS OF PHEXOLIC ALDEEYDES
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Reaction of p-hydroxybenzaldehyde with alkali and silver nitrate (Process II). To a wellstirred solution of 48.0 g. (1.2 moles) of sodium hydroxide and 24.4 g. (0.2 mole) of p-hydroxybenzaldehyde i n 400 cc. of water at 50" was added 34.0 g. (0.2 mole) of silver nitrate i n 50 cc. of water. An immediate reaction took place and the temperature rose considerably. The mixture was stirred for 30 minutes without heating and filtered. The precipitated spongy silver was washed with water and stored under water. The combined filtrate and washings were acidified with sulfur dioxide [use of nonreducing acids in this case gives nitro compounds (2)l to give 25.0 g. (90.6%) of p-hydroxybenzoic acid melting at 212-213'. The aqueous filtrate, upon saturating with sodium chloride and extracting with ether, yielded a n additional 2.6 g. (9.4%) of p-hydroxybenzoic acid melting at 207-209" which, upon crystallization from water, melted a t 212-213". Reaction of 5-chlorovanillin with alkali and less than 0.5 mole of silver oxide. Freshly prepared silver oxide (0.025 mole) was prepared in the usual manner from 8.25 g. of silver nitrate and 2.1 g. of sodium hydroxide. The filtered and washed oxide was covered with 800 cc. of water and treated with stirring with 40 g. (1.0 mole) of sodium hydroxide. This stirred suspension was heated to 60" and treated with 46.5 g. (0.25 mole) of 5-chlorovanillin, which caused reaction to set in and the temperature to rise. The mixture was heated to boiling under reflux with stirring for 30 minutes, filtered, and the silver precipitate waswashed with water. The combined filtrate and washings were acidified with carbon dioxide until acid t o phenolphthalein and extracted with ether. The ether was dried with sodium sulfate and distilled, leaving 18.1 g. (38.4%) 5-chlorovanillyl alcohol as a white powder melting at 95-97'. Repeated recrystallizations from petroleum ether or water gave white needles melting a t 110-111". Anal. Calc'd for C8H9C103: CI-110, 16.45. Found: C&O, 16.49. The carbonated aqueous solution was acidified further with sulfur dioxide. The white crystalline precipitate was filtered, washed with water and dried to give 29.4 g. (58.1%) of' 5-chlorovanillic acid melting a t 242-244'. Recrystallization from dilute acetic acid raised the melting point to 244-245". Extraction of the sulfur dioxide-saturated filtrate with ether yielded an additional 1.4 g. (3.0%) of 5-chlorovanillyl alcohol which, upon recrystallization from water, melted at 110-111". Reaction of p-hydroxybenzaldehyde with alkali i n the presence of active silver. A mixture of 24.4 g. (0.2 mole) of p-hydroxybenzaldehyde, 48.0 g. (1.2 moles) of sodium hydroxide, 21.6 g. (0.2 atom) of active silver metal (from the reduction of silver oxide with p-hydroxybenzaldehyde by Process I), and 400 cc. of water was heated t o boiling for 1 hour and allowed to cool. The mixture was filtered and the silver was washed with water. The combined cooled filtrate and washings were saturated with carbon dioxide and sodium chloride and extracted mith ether. The ether was dried and distilled under reduced pressure to give 11.7 g. (47.1%) of p-hydroxybenzyl alcohol as a white solid melting at 123-124". Recrystallization from mater yielded white crystals, m.p. 124-125'. The carbonated aqueous solution was further acidified with sulfur dioxide and extracted with ether to yield 13.0 g. (49.6%) of p-hydroxybenzoic acid as white platelets melting a t 208-210' which, upon recrystallization from water, melted a t 212-213". I n an alternate method the filtered allraline reaction mixture was acidified directly with sulfur dioxide, saturated with sodium chloride, and extracted with ether. The ether was dried and distilled. The residue was treated with excess 8% sodium bicarbonate solution and filtered. The precipitate, weighing 10.6g. (43.0y0),was aresinous condensed p-hydroxybenzyl alcohol and was insoluble in boiling water or benzene. Acidification of the bicarbonate solution yielded 13.0 g. (49.6%) of p-hydroxybenzoic acid melting at 208-210" which, upon recryetalliaation from water, melted at 212-213'. Reaction of salicylaldehyde with alkali and formaldehyde in the presence of active szlver. T o a vigorously agitated suspension of 10.8 g. (0.1 atom) of fluffy active silver (prepared by the reduction of silver oxide with salicylaldehyde) in 100 cc. of water was added 24.0 g.
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IRWIN A. PEARL
(0.6 mole) of solid sodium hydroxide. The temperature a t this point was 53". A mixture of 12.2 g. (0.1 mole) of salicylaldehyde and 50 cc. (0.5 mole) of 37% formalin was then added with continued agitation. Violent reaction set in and the temperature rose to 90". After 30 minutes of agitation, the mixture was heated t o boiling, allowed to cool, and filtered. The filtrate and washings were saturated with carbon dioxide and with sodium chloride and
TABLE I SILVERCATALYZED REACTIONS SILVER
ALDEHYDE
OXIDE (YOLE)
o-Vanillin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6-Chlorovanillin . . . . . . . . . . . . . . . . . 5-Chlorovanillin . ....................... 5-Chlorovanillin. . . . . . . . . . . . . . . . . . . . . . . . ...................
ACD,%
(MOLES)
--
ALCOHOL,
%
93.5 93.8 97.8 97.0
58.1 1.0d 1.0'
49.0 5.0
.5* .5= 1.0d 1.06 1.Of
98.6 99.0 50.0 61.6
5.0
.5b .5"
p-Dimethylaminobenzaldehyde a
FOFMALDEHYDE
0.5* .5" .5b .5c .I
5-Chlorovanillin , .......................
Salicylaldehyde, . . . . . . . Salicylaldehyde, ........................ Salicylaldehyde, ........................ Salicylaldehyde ................ Salicylaldehyde". ....................... p-Hydroxybenzaldehyde p-Hydroxybenzaldehyde" . . . . . . . . . . . . . . . p-Hydroxybenzaldehyde" . . . . . . . . . . . . . . p-Hydroxybenzaldehyde" . . . . . . . . . . . . . . . p-Hydroxybenzaldehyde. . . . . . . . . . . . . . . . p-Hydroxybenzaldehyde. . . . . . . . . . . . . . . . p-Hydroxybenzaldeh yde . . . . . . . . . . . . . . . .
SILVER (ATOM)
1. Odtf L.Od*f 1.06 1.0' 1.0' 1.oi
98.9 100.0 49.6 49.6 69.3
5.0 5.0 43.6
41.4 48.1 98.4
49.2 36.7 98.4
47.19 43. Oh 26.89 97.29 92, 8h 44.5i
Details in Experimental part.
* Silver oxide prepared according to Process I.
Silver oxide prepared in situ according to Process 11. Silver isolated from reaction of corresponding aldehyde according t o Process I. Silver isolated from reaction of corresponding aldehyde according t o Process 11. f Reuse of silver isolated from reaction of corresponding aldehyde according t o Process 11. 0 p-Hydroxybenzyl alcohol, m.p. 124-125". Resinous p-hydroxybenzyl alcohol calculated as p-hydroxybenzyl alcohol. ' Silver prepared by reduction of silver oxide by vanillin according to Process I . j pDimethylaminobenzy1 alcohol was not isolated pure but the crude product was treated with methyl iodide in acetone to give dimethylaminobenzyl alcohol methiodide, m.p. 231-232' (6). extracted with ether. The ether was dried and distilled under reduced pressure, yielding 12.2 g. (98.4%) of salicyl alcohol as white crystals melting a t 83-85'. Recrystallization from petroleum ether raised the melting point to 85-86'. All compounds listed in Table I, except 5-chlorovanillyl alcohol, have been previously prepared and recorded. I n all instances the melting points and properties of the compounds isolated in this study concurred with those in the literature.
REACTIONS OF PHENOLIC ALDEHYDES
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SUMMARY
Four 0- and p-hydroxy- and one amino-substituted benzaldehydes were subjected to reaction with alkali in the presence of either silver oxide or active silver metal. The reactions previously found to take place with vanillin also took place with these aldehydes. Cannizzaro and crossed Cannizzaro reactions of p-hydroxybenzaldehydeyielded either crystalline or resinous p-hydroxybenzyl alcohol, depending upon the experimental procedure. Active silver appears to be a universal catalyst for catalyzing the Cannizzaro reaction of aldehydes which are unaffected by alkali alone. 5-Chlorovanillylalcohol was prepared and identified. Reaction with alkali and 0.5 mole of silver oxide provides a simple laboratory method for the preparation of 0- and p-hydroxy-substituted benzoic acids from their corresponding aldehydes. APPLETONWIS. REFERENCES
PEARL, J . Am. Chem. SOC.,68, 429 (1946). PEARL, J. Am. Chem. Soc., 88,1100 (1946). PEARL, J . Org. Chem., 12,79 (1947). GEISSMAN,Chapter 3 in Adams “Organic Reactions,” John Wiley and Sons, New York, N. Y . ,1944, Vol. 11, pages 104-107. (5) For a preliminary announcement of this work see PEARL, J . Am. Chem. SOC.,67, 1628
(1) (2) (3) (4)
(6) (7) (8) (9)
(1945). CLEMOAND SMITH,J . Chem. SOC.,2423 (1928). BRAUNAND KRUBER,Ber., 46, 2978 (1912). RUPPA N D LINCK,Arch. Pharm., 253,39 (1915). MENKE:A N D BENTLY, J.Am. Chem. Soc., 20,316 (1898).
