Acetals from dihalides

A suspension of lead oxide in water is used in the preparation of 2,3 butanediol from the corresponding dibromide. Glycols are usually obtained from dihalides through the acetates (method 93). 

The products of these reactions are called vicinal dihalides Two substituents m this case the halogens are vicinal if they are attached to adjacent carbons The word is derived from the Latin vicinalis which means neighboring The halogen is either chlorine (CI2) or bromine (Br2) and addition takes place rapidly at room temperature and below m a variety of solvents mcludmg acetic acid carbon tetrachloride chloroform and dichloromethane... 

Monoalkylthallium(III) compounds are unstable (73, 79), and very few examples of this class have been isolated. A number of alkylthallium diacetates have been obtained either from oxythallation of olefins with thallium-(III) acetate (see below) or from exchange reactions such as that shown in Eq. (11) (74, 75). Only four alkylthallium dihalides have been isolated so far, namely a neopentylthallium dihalide (60) [Eq. (12)] and the isomeric 2-, 3-, and 4-pyridiomethylthallium dichlorides (20) [Eq. (13)]. Monoaryl-and monovinylthallium(III) derivatives are considerably more stable than... 

Acetate pyrolysis is illustrated by the synthesis of penta-1,4-diene (Expt 5.14) from 1,5-diacetoxypentane. This is prepared from 5-chloropentyl acetate which is conveniently obtained from tetrahydropyran by treatment with acetyl chloride this ring-opening reaction offers interesting comparison with the methods for the preparation of a, cu-dihalides discussed in Section 5.5.1, p. 555. 

Replacement of the Halogen at Carbon Atom 1.—From the acetyl-dihalide derivative, the acetates of the 2-desoxy-2-halogeno-aldoses can be prepared by treatment with moist silver carbonate or oxide. 

Higher-valent metal halides oxidize diaryl tellurium compounds to diaryl tellurium dihalides. Copper(II) halides can be generated in the reaction mixture from easily accessible copper(II) acetate and hydrohalic acids4. These halogenation reactions are convenient alternatives to the methods using corrosive elemental halogens or sulfuryl halides. 

Thus, for example, the direct conversion of an ether into an acetal or ketal is difficult to achieve whereas the oxidation of an alcohol to an aldehyde or ketone (or the reverse process) is a trivial transformation. Similarly, the transition from an oxidation level of 2 to level 1 is problematic in the case when one tries to convert dihalides into monohalides while the transformation of alkynes into alkenes may be safely considered a viable route to carry out this transition. 

Alkenes (e.g. camphene) are readily prepared by the BF3,Et20-catalysed elimination of secondary borate esters.Terminal conjugated dienes may be prepared by Pd(OAc)2-PPh3-catalysed elimination from allyl phenyl ethers or allylic acetates [e.g. geranyl, neryl, and linalyl acetates to form similar mixtures of myrcene (60—74%), trans-ocimene (8—20%), and c -ocimene (14—20%)], and the complex [(i7-CsH5)Cr(NO)2]2 dehalogenates n/c-dihalides (e.g. limonene tetrabromide) without affecting other halides (except for benzyl halides). 

Compounds containing In—O, In—S, and In—Se Bonds.— A number of compounds derived from In acetate have been studied by Habeeb and Tuck. Among these was indium diacetate, produced by the electrolysis of In in acetic acid. This has a lattice of In(OAc)3 + In(OAc), containing polymeric carboxylate-bridged units [similar to In(OAc)3, (Me4N)3ln(OAc>3 (C104)3, etc., which is unrelated to the indium dihalides . 

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