View Article Online / Journal Homepage / Table of Contents for this issue THE OXIDATION OF MONOHY DRIC PHENOLS. 1659 Published on 01 January 1910. Downloaded by University of Illinois at Chicago 03/02/2015 08:14:15. CLV.-The Oxiclation of Monohyd& Phenols with Hydcrogen Peroxide. By GEORGEGERALD HENDERSON and ROBERTBOYD, B.Sc. (Carnegie Research Scholar). HAVINGoccasion to prepare some dihydric phenols of the formula, C,,H,,(OH),, we endeavoured to find a simpler and more direct method of obtaining these compounds from monohydric phenols than those which are usually employed. To begin with, we applied to thymol the process of oxidising monohydric phenols in alkaline solution with potassium persulphate, which is stated to work well with the lower members of the series, but the results were not satisfactory, Equally disappointing results attended our trials of View Article Online 1660 HENDERSON AND BOYD: THE OXIDATION OF the method of oxidation with dilute solutions of hydrogen peroxide, but the use of Merck’s “ perhydrol,” a 30 per cent. aqueous solution of hydrogen peroxide, led to the attainment of the desired end. A number of monohydric phenols of the benzene series were treated with this reagent, glacial acetic acid being used as a solvent for the phenol, and all were found to undergo oxidation more or less easily, either in t?he cold 01- when moderately heated. The product was either a quinone, from which, of course, the corresponding dihydric phenol could be obtained by reduction, or a dihydric phenol, or, in one or two cases, a tetrahydric phenol. The following is a statement of the phenols examined and of the products obtained from them under the conditions described below. Thymol gave a very good yield of thymoquinone, along with a small quantity of a new tetrahydric phenol, tetraJcydr*ox~c~me?i?e, C,MePrS(OH),, a, colourless, crystalline solid, melting at 168O. Carvacrol gave the same products as thymol, in approximately the same relative proportions. 3 : 5-Diethylphenol, C,H,E&-OH, gave, apparently as sole product, the corresponding 3 : 5-dietJ~?/Z-p-beizzop~inone,C,H,Et,Oz, golden- yellow needles, melting at 36O, from which, by reduction with sulphurous acid, the dihydric phenol, 3 : 5-dietlT~ylquinoZ, C,H,Et,( OH),, was obta.ined in colourless crystals, melting at 114O. p-Nitroso-3 : 5-diethyZpJ~enoZwas also prepared. It forms pale yellow crystals, melting at 136O, and on reduction and subsequent oxidation yields diethyl-p-benzoquinone. p-tert.-Butylphenol, CsH4(CMe3)*OH, gave a new tetrahydric phenol, t etrahydroq-tert .-b utylb cnzcne, CGH(CMe,)(OH),, which crystallises in slender, colourless needles, melting at 138O. Phenol gave quinol, a little p-benzoqdinone, and a little catechol ; Published on 01 January 1910. Downloaded by University of Illinois at Chicago 03/02/2015 08:14:15. no resorcinol was found. o-Cresol gave toluquinol (2 : 5-dihydroxytoluene) and some tolu- quinone ; m-cresol gave toluquinol, some toluquinone, and a little orcinoI ; and p-cresol gave homocatechol (3 : 4-dihydrosytoluene) ; no other product was found. The character of the oxidation products obtained depended, in the first place, on the constitution of the phenol oxidised, and, in the second place, on the conditions of the experiment, namely, the proportion of perhydrol used, the concentration of the acetic acid solution, the temperature, and the time. As regards the first point, it was found that monoliydric phenols, in which the p-position relative to the hydrosyl radicle is unoccupied by a radicle other than hydrogen, are more or less easily attacked by hydrogen per- oxide even at the ordinary temperature, and that the product of oxidation is mainly a quinone, or a p-dihydric phenol, or a mixture View Article Online MONOHPDRIC PHENOLS WlTH HYDROGEN PEROXIDE. 1661 of both, according to the conditions under which the reaction is carried out. On the other hand, those monohydric phenols in which the p-position relative to the hydroxyl group is occupied are osidised with greater difficulty, and a higher temperature is neces- sary; in such cases the product is usually a dihydric phenol con- taining the hydroxyl groups in the o-position with respect to each other. The lower members of the series tend to give tarry products more easily than the higher members, and it is best to use a larger proportion of the solvent (acetic aoid) when the former are being oxidised. We have also examined the action of perhydrol on smne cyclic hydrocarbons. In each case the hydrocarbon was mixed with per- hydrol, sufficient acetic acid to €orm a clear solution was added, and the liquid was left for some time at the ordinary temperature or gently heated. The inembers of the benzene series which were used, namely, benzene, toluene, 1 : 3-diethylbenzene, and cymene, did not appear to react at all easily with the oxidising agent, but naphthalene, anthracene, and phenanthrene were readily oxidised, yielding phthalic acid, anthraquinone, and phcnanthraquinone respectively. The course of the preparative work invoIved in this investigation led us to attempt to prepare higher dihydric phenols directly by condensing quinol and resorcinol with diethyl ether in presence of anhydrous aluininium chloride. These experiments were unsuccess- ful, but we found that phenol could be condensed with methyl propyl ether, yielding a substance which appears to be a methylpropyl- phenol, C,H3MePr-OH. We intend to continue to study the behaviour of hydrocarbons towards perhydrol, and also to extend our experiments to Published on 01 January 1910. Downloaded by University of Illinois at Chicago 03/02/2015 08:14:15. derivatives of phenols and to phenols other than those of the benzene series. EXPERINENTAL. According to a patented process (D.R.-P. 81068 and 81298), dihydric phenols of the benzene series can be obtained on the manufacturing scale from monohydric phenols by means of potassium persulphate. The persulphate is added in small portions to a dilute alkaline solution of the phenol, and the liquid is kept for one or two days at the ordinary temperature, or at 40°. When the reaction is finished, the solution is saturated with carbon dioxide, any unchanged phenol is distilled off in a current of steam, the residual liquid is acidified with dilute acid and then boiled, and finally the dihydric phenol which has been formed is extracted with ether. If the p-position relative to the hydroxyl group in the monohydric phenol is free, a p-dihydroxy-compound is obtained, View Article Online 1662 HENDERSON AND BOYD: THE OXlDATlON OF but if the p-position is occupied, the product contains two hydroxyl groups in the o-position with respect to each other. Thus, phenol yields quinol, whilst p-cresol yields homocatechol. As the process appeared to be a pra.cticable one, we applied it in the prescribed manner to the oxidation of thymol, but found that with that compound the reaction does not proceed smoothly, as in the case of lower phenols. Much of the thymol remained unattacked, whilst the rest was mainly converted into a tarry substance, from which it was scarcely possible to separate any definite oxidation product. Various modifications of the process were tried-such as keeping the mixture cool with ice; adding the persulphate to a solution of thymol in the least possible quantity of alkali, and maintaining the mixture slightly alkaline by addition of sodium carbonate from time to time; agitating a mixture of thymol with aqueous potassium persulphate for several days, both at the ordinary temperature and at 60°-but with no improvement in the results. A dilute solution of hydrogen peroxide, either with or without the addition of a small quantity of an iron salt., has frequently been used as an oxidising agent, and, according to Martinoil (BUZZ. SOC. chim., 1885, [ii], 43, 155), when dilute aqueous hydrogen peroxide is gradually added to pure phenol in the cold, and the liquid is subsequently heated to 90°, oxidation of the phenol takes place, and a mixture of quinol, p-benzoquinone, and catecho1 is obtained. With thymol, however, we found this process also to be unsatisfac- tory; using ordinary '' ten volume " hydrogen peroxide, according to Martinon's method, very little of the thymol wits attacked, even when the mixture was heated. It then occurred to us to try a stronger solution of hydrogen peroxide, and this led to success. It Published on 01 January 1910. Downloaded by University of Illinois at Chicago 03/02/2015 08:14:15. was found that thymol and other monohydric phenols, when dis- solved in glacial acetic acid, are more or less readily oxidised by perhydrol, with the results described in the following pages. Oxidation of Thyrno~?ur'tli PerhydroL-Seventy-five grams of thymol (1 mol.) were mixed with 190 C.C. of perhydrol (about 2 mols.), sufficient acetic acid was added to hold the thymol in solution, and the mixture was kept at the ordinary temperature. After a week or two, a small quantity of a colourless, crystalline solid had separated from the solution. The solid was collected, and water was gradually added to the filtrate until no further pre- cipitation took place. The yellow, crystalline precipitate was agitated with dilute sodium hydroxide, when only a small part passed into solution, and the undissolved portion was collected, washed with water, and dried. The golden-yellow crystals obtained in this way melted at 45*5O, and were identified as thymoquinone. View Article Online MOKOHYDRIC PHENOLS WITH HYDROGEN PEROXIDE. 1663 A small additional quantity of thymoquinone was obtained from the mother liquor by steam distillation. Only a little of the thymol remained unoxidised. The alkaline solution with which the thymoquinone had been washed gave, on acidification, a precipitate of a, crystalline com- pound, which proved to be identical with the substance which had crystallised from the original acetic acid solution.