Halogenation of aliphatic acids

The stoichiometry and promotional role of chlorosulfonic and fuming sulfuric acids in the a-halogenation of aliphatic acids were examined. In a-bromination or iodination with bromine or iodine respectively, 1 mole of halogen produces 2 moles of the a-haloacid, whereas in the analogous chlorination 1 mole of chlorine... 

Chlorosulfonic acid, as well as catalysing the a-halogenation of aliphatic acids, also functions as an acidic dehydration catalyst which can be valuable in the esterification of carboxylic acids. 

Two different sets of experimental conditions have been used. Buu-Hoi et al. and Hansen have employed the method introduced by Papa et using Raney nickel alloy directly for the desulfurization in an alkaline medium. Under these conditions most functional groups are removed and this method is most convenient for the preparation of aliphatic acids. The other method uses Raney nickel catalysts of different reactivity in various solvents such as aqueous ammonia, alcohol, ether, or acetone. The solvent and activity of the catalyst can have an appreciable influence on yields and types of compounds formed, but have not yet been investigated in detail. In acetic anhydride, for instance, desulfurization of thiophenes does not occur and these reaction conditions have been employed for reductive acetylation of nitrothiophenes. Even under the mildest conditions, all double bonds are hydrogenated and all halogens removed. Nitro and oxime groups are reduced to amines. 

Decarboxylativehalogenation (12,417). The Hunsdiecker reaction is not useful for aromatic acids, but decarboxylative halogenation of these acids can be effected in useful yield by radical bromination or iodination of the thiohydroxamic esters, as reported earlier for aliphatic acids.1 Thus when the esters 2 are heated at 100° in the presence of AIBN, carbon dioxide is evolved and the resulting radical is trapped by BrCCl3 to provide bromoarenes (3). Decarboxylative iodination is effected with iodoform or methylene iodide as the iodine donor. 

Perhaloalkanes serve as bromination or iodination agents in the radical decarbox-ylative halogenation of carboxylic acids. In an interesting modification of the Hunsdiecker-Bodin reaction Barton and coworkers have applied iV-hydroxypyridine-2-thione esters as nonelectrophilic intermediates for the decarboxylative bromination and iodination of primary, secondary and tertiary aliphatic and alicyclic592, as well as aroma-... 

The great chemical resistibility of aliphatic hydrocarbons and the aggregate1 state of their members poor in carbon make them appear us unsuitable material for eleotrolytical experiments. Only the addition-reactions of unsaturated hydrocarbons offer an experimental field. This has not yet been developed. These reactions are cathodic in the addition of hydrogen, and anodic in the addition of halogens, etc. The fact that such hydrocarbons occur in the decomposition of aliphatic acids gives us an indication as to their behavior, which will he mentioned at the proper place. 

Direct chlorination of acetic acid in the presence of a small quantity of red phosphorus is a standard procedure for the preparation of chloro-acetic acid however, similar treatment of its straight-chain homologs gives complex mixtures of halogenated acids. Substitution by chlorine in a btanched-chain acid such as isovaleric acid occurs largely at the tertiary hydrogen. The peroxide-catalyzed chlorination of aliphatic acids... 

Halogen in positions other than next to the carboxyl group of aliphatic acids is somewhat less reactive. For preparation of methyl 4-(diethylamino)-butyrate from the 4-chloro compound the detour through the 4-iodo compound was chosen, this being easily accessible by means of sodium iodide.521... 

Electroreduction of styrenes or alkyl methacrylates in the presence of aliphatic acid anhydrides or N-acylimidazoles with zinc anode brought about novel one-pot vicinal double C-acylation to afford the corresponding 1,4-diketones in good to high yields. This is an example of cross-coupling reaction with no use of halogenated compounds. 

The general mechanism of the acid-catalysed a-halogenation of aliphatic carboxylic acids (87) may be summarized by Equations 51-53. The adduct (131 X = I) was found to regenerate iodine consequently, 1 mole of iodine yields 2 moles of the a-iodoacid, a similar effect presumably occurs in bromination. 

It is frequently advisable in the routine examination of an ester, and before any derivatives are considered, to determine the saponification equivalent of the ester. In order to ensure that complete hydrolysis takes place in a comparatively short time, the quantitative saponi fication is conducted with a standardised alcoholic solution of caustic alkali—preferably potassium hydroxide since the potassium salts of organic acids are usuaUy more soluble than the sodium salts. A knowledge of the b.p. and the saponification equivalent of the unknown ester would provide the basis for a fairly accurate approximation of the size of the ester molecule. It must, however, be borne in mind that certain structures may effect the values of the equivalent thus aliphatic halo genated esters may consume alkali because of hydrolysis of part of the halogen during the determination, nitro esters may be reduced by the alkaline hydrolysis medium, etc. 

N-Benzylamides are recommended when the corresponding acid is liquid and/or water-soluble so that it cannot itself serve as a derivative. Phe benzylamides derived from the simple fatty acids or their esters are not altogether satisfactory (see Table below) those derived from most hydroxy-acids and from poly basic acids or their esters are formed in good yield and are easily purified. The esters of aromatic acids yield satisfactory derivatives but the method must compete with the equally simple process of hydrolysis and precipitation of the free acid, an obvious derivative when the acid is a solid. The procedure fails with esters of keto, sul phonic, inorganic and some halogenated aliphatic esters. 

In addition to its water solubility poly(vinyl pyrrolidone) is soluble in a very wide range of materials, including aliphatic halogenated hydrocarbons (methylene dichloride, chloroform), many monohydric and polyhdric alcohols (methanol, ethanol, ethylene glycol), some ketones (acetyl acetone) and lactones (a-butyrolactone), lower aliphatic acids (glacial acetic acid) and the nitro-paraffins. The polymer is also compatible with a wide range of other synthetic polymers, with gums and with plasticisers. 

The action of chlorine on the aliphatic acids takes place in presence of sunlight, also on the addition of small quantities of the halogen-carriers, iodine, sulphur, and red phosphorus. By the action ofiodine, I Cl is formed, which decomposes moie readily than the molecule of chlorine, and hydriodic acid is libciatcd,... 

The effect of introducing electron-withdrawing substituents into simple aliphatic acids is more marked. Thus halogen, with an inductive effect acting in the opposite direction to alkyl, might be expected to increase the strength of an acid so substituted, and this is indeed observed as pKa values show ... 

Figure 2 shows a simplified process flow diagram for halogenated aliphatic acid production facilities [8]. Halogenated aliphatic acids include chlorinated aliphatic acids and their salts, for example, TCA, Dalapon, and Fenac herbicides. Chlorinated aliphatic acids can be prepared by nitric acid oxidation of chloral (TCA) or by direct chlorination of the acid. The acids can be sold as mono- or dichloro acids, or neutralized to an aqueous solution with caustic soda. The neutralized solution is generally fed to a dryer from which the powdered product is packaged. 

As shown on Figure 2, wastewaters potentially produced during the manufacture of halogenated aliphatic acids include the following ... 

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