LX I ' I I.-Some Derivatives of Anh y dram t onebemil.

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The standard methods of separately determining aldehydes in mixtures such as those obtained from combustion of hydrocarbons have proved unsatisfactory. A method is described in which the aldehydes are oxidised by silver oxide to the silver salts of fatty acids. The silver is determined volumetrically by potassium thiocyanate. Separation and determination of individual aldehydes is achieved by chromatography of the acids which can be liberated from the silver salts. The method has been successfully applied to the identification and determination of the aldehydes formed during the oxidation of higher hydrocarbons.DURING research into the products of hydrocarbon combustion several difficulties were encountered in the determination of aldehydes owing to interference from some of the other products of the reaction. The standard method using hydroxylamine hydrochloride, although giving accurate results with pure samples, is not specific for aldehydes but determines ketones also.Peroxides cause serious interference and, in agreement with Smith and Mitchell ( A nalyt. Chem., 1950, 22, 750), we have found that the discrepancy amounts to between two and four times the amount of peroxide present, depending upon the temperature and time of standing.In addition weak acids, if present in quantity comparable with that of the aldehydes, lead to uncertain results owing to their buffering action.A modification of Ripper's bisulphite method described by Siggia and Maxcy (Ind. Eng.Chem., Anal., 1947, 19, 1023) has also been tried. Although hydrogen peroxide does not interfere when in small concentration, tertiary butyl hydroperoxide liberates approximately one molecule of alkali for every two of peroxide present and so leads to high results.When analysing combustion products we have found that a method based on the oxidising action of silver oxide on aldehydes is more satisfactory. Aldehydes are thus oxidised to fatty acids which then dissolve more oxide to form salts, the silver in which may readily be determined by titration with potassium thiocyanate. Smith and Mitchell (AnaZyt. Chem., 1950, 22, 746) have recently described a method similar to ours in which the aldehydes are heated to 60' with silver oxide in a stoppered flask ; standard sodium hydroxide is added to precipitate the silver and the excess is back-titrated with hydrochloric acid. This method, however, suffers from the disadvantage that acetaldehyde and formaldehyde are only partially estimated. The method described below has been tested with these aldehydes amongst others and gives results which are accurate to within 2% for straight-chain saturated aliphatic aldehydes up to hexanoic. Not only is the silver oxide method of use for aldehydes where other methods may fail owing to interference, but it can also be made a basis for the quantitative separation and determination of individual aldehydes in mixtures. The fattyacids can be prepared from the silver salts and then separated by chromatography whereas there is no simple method of analysing a mixture of aldehydes ...

Basic Properties of Oxygen in Organic Acids and Phenols; and the Quadrivalency of Oxygen.