Sulphurous Acid, Reaction Ketones with

The preparation of 4-methylcoumarin is an example of the Pechmann reaction, which consists in the interaction of a phenol with a 3-ketonic ester In the presence of a condensing agent (sulphuric acid, aluminium chloride, phosphorus oxychloride or pho.sphoric oxide) ... 

A further improvement is embodied in the Klndler variation of the Willgerodt reaction this consists in heating the ketone with approximately equal amounts of sulphur and a dry amine instead of aqueous ammonium polysulphide. The principal product is a thioamide, and hydrolysis with acid or alkali affords the carboxylic acid, usually in good yield. 

It is convenient to consider the indifferent or neutral oxygen derivatives of the hydrocarbons—(a) aldehydes and ketones, (b) esters and anhydrides, (c) alcohols and ethers— together. All of these, with the exception of the water-soluble members of low molecular weight, are soluble only in concentrated sulphuric acid, t.e., fall into Solubility Group V. The above classes of compounds must be tested for in the order in which they are listed, otherwise erroneous conclusions may be drawn from the reactions for functional groups about to be described. 

The colour reaction with fuchsine-sulphurous acid provides a means of distinguishing sharply between aldehydes and ketones. In dilute aqueous solution dextrose reacts negatively. Concerning the mechanism of the colour reaction see Ber., 1921, 54, 2527. 

Early electrochemical processes for the oxidation of alcohols to ketones or carboxylic acids used platinum or lead dioxide anodes, usually with dilute sulphuric acid as electrolyte. A divided cell is only necessary in the oxidation of primary alcohols to carboxylic acids if (he substrate possesses an unsaturated function, which could be reduced at the cathode [1,2]. Lead dioxide is the better anode material and satisfactory yields of the carboxylic acid have been obtained from oxidation of primary alcohols up to hexanol [3]. Aldehydes are intermediates in these reactions. Volatile aldehydes can be removed from the electrochemical cell in a... 

Reaction XXIV. Condensation of certain Carbonyl Compounds with one another under the influence of Dehydrating Agents. (A., 223, 139.)— Aldehydes and ketones readily condense with one another under the influence of such reagents as zinc chloride, hydrochloric acid, sulphuric acid, alkali hydroxides, sodium acetate solution, etc., to give a/J-olefinic aldehydes and ketones ... 

Reaction LXVH. (a) Ketonic Hydrolysis of Alkyl Derivatives of Ethyl Acetoacetate. (A., 138, 211.)—This reaction illustrates one of many synthetical uses of acetoacetic ester. When that ester or its mono- or dialkyl derivatives is boiled with dilute aqueous or alcoholic alkalis or baryta water, or sulphuric acid, ketonic hydrolysis occurs, and acetone or its mono- or di-substituted derivatives is formed—... 

The oxidation of secondary alcohols with sodium dichromate in dilute sulphuric acid gives acceptable yields of ketones since these do not normally undergo extensive further oxidation under the reaction conditions (cf. Section 5.7.1, p. 587, the oxidation of primary alcohols to aldehydes). 

The direct hydration of a terminal alkyne, with dilute sulphuric acid in the presence of a mercury salt, yields initially an enol which rearranges to the more stable ketone. The regioselectivity of the reaction is consistent with that predicted on the basis of mechanistic theory. 

To an ice-cold mixture of 1.0 ml of concentrated sulphuric acid and 5 ml of saturated aqueous potassium dichromate solution, add 2 ml of the alcohol or its concentrated aqueous solution. If the alcohol is not miscible with the reagent, shake the reaction mixture vigorously. After 5 minutes, dilute with an equal volume of water, distil and collect the first few ml of the aqueous distillate in a test tube cooled in ice. (Aldehydes and ketones are volatile in steam.) Test a portion of the distillate for a carbonyl compound with 2,4-dinitrophenylhydrazine reagent (p. 1218). If a solid derivative is obtained, indicating that the compound was a primary or secondary alcohol, test a further portion with SchifFs reagent (p. 1291) to distinguish between the two possibilities. The derivative may be recrystallised the m.p. may give a preliminary indication of the identity of the alcohol. 

Epoxides can be synthesised by the action of aldehydes or ketones with sulphur-ylides. They can also be prepared from alkenes by reaction with m-chloroperoxybenzoic acid. 

Many reactions of ketones were performed with methanolic DIB in either an acidic or alkaline environment. When DIB is dissolved in methanol (or other alcohols) an exchange with acetate takes place, so that the reacting species may be PhI(OMe)OAc or PhI(OMe)2 the latter is actually an isolable compound [12]. Oxidation of methanol at room temperature is negligible. Acetophenones react with DIB in methanol-sulphuric acid affording mixtures of a-methoxyacetophenones (minor products) and rearranged esters. A solvent change from methanol to... 

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