Preparation haloform reaction

The haloform reaction is sometimes used for the preparation of carboxylic acids from methyl ketones... 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

The haloform reaction is a useful method of preparing a carboxylic acid (carboxylate ion) with one less carbon. It is one of the very few cases where carbanion loss occurs. It s only possible because the three halogen atoms are capable of stabilizing the negative charge. 

Problem 16.8 (a) Why isn t 2-naphthoic acid made from 2-chloronaphthalene (f>) How is 2-naphthoic acid prepared in a haloform reaction M... 

Of the disubstituted tetrahydronaphthalenes (V and VI), only Vic is a new compound, but Va was prepared by a new process. Furthermore, we had completed our synthesis of Vb before the appearance of the almost identical preparation of O Fabrell et al. [3] The hydroxyketone VI6 was prepared by the general method of O Farrell et al. [3], but our synthesis proceeded in much higher yield. Some unique results also have been obtained by subjecting 3-methoxy-5,6,7,8-tetrahydro-2-aeetonaphthone to the haloform reaction. 

Hi) Carboxylic acids and derivatives. The haloform reaction on thienyl methyl ketones leads to thiophenecarboxylic acids, which can be treated with Raney nickel to produce the open-chain acids. This method has been used for the five-carbon homologation of carboxylic acids and to produce dicarboxylic acids (Scheme 51). Long-chain carboxylic acids may also be prepared by using dicarboxylic acid derivatives for the acylation of thiophenes (Scheme 52). In the synthesis of Queen substance, the precursor (213) has been generated by Raney nickel desulfurization of the appropriate thiophene-2-acetic acid derivative (79T329). 

Because the haloform reaction is fast, in some cases it can be used to prepare unsaturated acids from unsaturated ketones without serious complications caused by addition of halogen to the double bond ... 

To retain a side-chain substituent, selective methods of oxidation are required. For example, 4-methylbenzoic acid can be prepared from l-(4-methylphenyl)-ethanone by the haloform reaction (Section 17-2B) ... 

SYNTHESIS OF ALKYL PROPANOATES BY A HALOFORM REACTION OF A TRICHLORO KETONE PREPARATION OF ETHYL 3,3-DIETHOXYPROPANOATE (Propanoic acid, 3,3-dlethoxy-, ethyl ester)... 

Synthesis of Alkyl Propanoates by Haloform Reaction of Trichloro Ketones Preparation of Ethyl 3,3-Diethoxypropanoate... 

Addition of bromochlorocarbene (carbenoid) to an alkene results in the formation of 1-bromo-1-chlorocyclopropanes. The preparative value of this process depends on the structure of the carbene source, the type of base used for a-elimination of hydrogen bromide from the haloform, reaction conditions etc. 

Alkali cleaves, a ,a>trihalomethyl ketones to trihalomethanes and carboxylic acids. This haloform reaction 714 also occurs directly if alkaline hypohalite solution is allowed to react with a methyl ketone and has preparative importance as a method of obtaining carboxylic acids from methyl ketones. 

Which of the following would be the most suitable starting material for the preparation of a carboxylic acid by the haloform reaction Give the structure of the carboxylic acid. 

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