Halides, alkyl from carbon tetrachloride

The present procedure seems to be a general one for producing alkyl halides from acids. To aid in isolating higher-boiling or solid products, solvents such as carbon tetrachloride and cyclohexane can be used.7 In preparing a solid, the mercuric halide can be removed by extraction with 5% potassium iodide. 

The Hunsdiecker reaction is a free-radical reaction for the synthesis of an alkyl halide. The starting material comes from the reaction of a silver carboxylate with a solution of a halogen in a solvent such as carbon tetrachloride (see Figure 12-44). The overall free-radical mechanism is shown in Figure 12-45. 

Halogenations with dihalotriphenylphosphoranes have been reviewed briefly by Fieser and Fieser.4 Dibromotriphenylphos-phorane appears to have been studied somewhat more than the dichloro compound, but both reagents effectively convert alcohols to alkyl halides, carboxylic acids and esters to acid halides, etc. The reaction of 1,2-epoxycyclohexane with dibromotriphenylphos-phorane under conditions similar to those described here gives a mixture of cis- and trans-1,2-dibromocyclohexanes. A reagent prepared from triphenylphosphine and carbon tetrachloride has been used for similar transformations.5... 

Simple alkyl halides respond to the common characterization tests in the same manner as alkanes they are insoluble in cold concentrated sulfuric acid they are inert to bromine in carbon tetrachloride, to aqueous permanganate, and to chromic anhydride. They arc readily distinguished from alkanes, however, by qualitative analysis (Sec. 2.25), which shows the presence of halogen. 

In the preparation of hydrocarbons an alkyl, aryl, or aralkyl halide is mixed with an excess of an aromatic hydrocarbon, and anhydrous aluminum chloride is added in small portions. The reagents must be free from moisture. If the reactants are not liquid or the reaction is very vigorous, a solvent is used. Benzene, nitrobenzene, carbon disulfide, or o-dichlorobenzene may be employed as solvents. When polyhalides are used, more than one molecule of the hydrocarbon may react. For example, benzene with chloroform yields triphenylmethane, and benzene with carbon tetrachloride gives triphenylmethyl chloride ... 

If a carbonium ion were involved, we should expect the halide to be derived from the more stable, and therefore the more highly branched, alkyl group. It is also pertinent that anisole is not cleaved by dry hydrogen chloride or hydrogen bromide in carbon tetrachloride solution unless a small amount of pyridine, dimethylaniline, or aniline is added.18 Furthermore, the presence of these bases increases the rate of cleavage of ethers in acetic acid solution. All these experiments imply that more than two molecules participate in the formation of the transition complex leading to etherification or cleavage (see p. 83). 

Allyl chloride reacts without rearrangement. Vinyl chloride does not react. The various polyhaloalkanes behave differently from each other carbon tetrachloride is almost as reactive as alkyl halides, chloroform requires heating under reflux, methylene dichloride reacts only on prolonged heating at 100° diphosphonylation is not observed even with 1,4-dichloroalkanes.190,191... 

Papaverine crystallizes from ethanol as rhombic prisms or small white needles melting at 147-148°C. It is readily soluble in hot benzene, glacial acetic acid, ethanol, or petroleum ether, sparingly soluble in ether and carbon tetrachloride, and almost insoluble in water. It is a weakly monoacidic base and forms many salts with common acids, and metallic double salts. With alkyl halides, sulfates, etc., papaverine yields quaternary salts a number of addition products with acyl halides have also been described. 

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