Halogen derivatives, preparation

Halogen derivatives of silanes can be obtained but direct halogena-tion often occurs with explosive violence the halogen derivatives are usually prepared by reacting the silane at low temperature with a carbon compound such as tetrachloromethane, in the presence of the corresponding aluminium halide which acts as a catalyst. 

Halogenation. Halogens and halogen acids add readily to the unsaturated carbon linkages of the cyclopentadiene molecule. By such additions a series of halogenated derivatives range, in the case of the chloride, from 3-chlotocydopentene to tetrachlorocyclopentane. Of all the possible chloto derivatives of CPD, only hexachlorocyclopentadiene [77-47-4] ever reached commercial status. It was used as an insecticide, but this use has been discontinued because of its toxicity (see Chlorocarbons and chlorohydrocarbons, toxic aromatics). It can be prepared by a Hquid phase chlorination of CPD below 50°C (29). 

Anth nthrones. Halogenated derivatives have been developed to improve the dyeing properties of anthanthrones, which have low tinctorial strength and poor affinity to cellulose fibers. The only example of commercial significance is Cl Vat Orange 3 [4378-614] (4) Cl 59300). This compound is prepared from l,l -dinaphthyl-8,8 -dicarboxyhc acid (173) with oleum and bromine as follows ... 

The most versatile method of preparing ethers is the Williamson ether synthesis, particularly in the preparation of unsymmetrical alkyl ethers (12,13). The reaction of sodium alcoholates with halogen derivatives of hydrocarbons gives the ethers ... 

Dialkyl sulfates can replace the halogen derivatives, and this modification is especially useful for the preparation of phenoHc ethers ... 

Amongst synthetic quinoxalines, numerous types of biological activity have been reported. 5,6,7,8-Tetrachloroquinoxaline (132) and related halogenated derivatives have found use in fungicidal formulations. Phosphoric esters of 6-hydroxyquinoxaline (133) have found use in insecticidal preparations, and phosphoric ester derivatives of 2-hydroxyquinoxalines, such as (134), function as anthelmintics. 

The reaction of methane tricarboxylate with indoline 342 gave the tricyclic derivative 361 which can be transformed to the amide derivatives 362 (97JHC969). Alkylation of the iV-benzyl indoline 360 with pentafluor-oacetone gave 363 which upon debenzylation and subsequent acylation with diketene followed by cyclization gave 364. Other haloacetones were used to prepare different halogenated derivatives (79BEP872311) (Scheme 63). 

No crystalline halogen derivatives of cedrene have been prepared, only liquid compounds being obtained when the sesquiterpene is treated by the usual processes. 

Exhaustive chlorination of 101 gave a mixture of polychloro derivatives with the 2,3,7,8-tetrachloro species as the major product. To achieve such C-halogenation it is necessary to choose a reaction medium that avoids hydrolysis of the initially formed 5-halides to 5-oxides [76USP3989715 90AHC(48)301]. The 1-halogenated derivatives of 100 and 101 can be readily prepared from the lithiated species (84MI14). 

Butyl rubber (a copolymer of isobutylene and 1-3 mole per cent isoprene) and its halogenated derivatives have unsaturation in the carbon-carbon backbone and consequently do not have as good aging properties as EPDM. There are also reports (9-12) that ozone-resistant butyl rubber with a high degree of unsaturation can be prepared by copolymerization of isobutylene with either cyclopentadiene or 9-pinene. 

Another route to the preparation of Cgo derivatives involves the reaction of a halogen derivative of diethylmalonate in the presence of a strong base with fullerenes, which results in a... 

A modification of the Pomeranz-Fritsch synthesis <1983JCXI3344> is used in the preparation of thieno[2,3- l-pyridine and its 2-substituted derivatives. An aryl aldehyde undergoes condensation with aminoacetaldehyde dimethyl acetal giving a Schiff base which cyclizes to form an imine product. The imine is treated with ethyl chloroformate followed by triethyl phosphate to form an intermediate carbonate-phosphonate, which then cyclizes to the thienopyr-idine product (Scheme 22) <2004S1935>. Very low product yields (2-17%) are obtained for alkyl- and phenyl-substituted thieno[2,3- ]pyridines however, the unsubstituted product and 2-halogenated derivatives give moderate yields (28-44%). 

The fully aromatic and unsubstituted pyrimido[ 1,2-6 ]pyridazinium perchlorate (171) has been prepared by the condensation of 3-aminopyridazine (170) with 1,1,3,3-tetraethoxypropane in the presence of polyphosphoric acid. The product was precipitated from the reaction mixture by treatment with perchloric acid and ice. Several alkyl, aryl and halogenated derivatives of this ring system have also been prepared (71JOC2457). 

---