Ethers dialkyl, bromination

Bromination of dialkyl ethers affords bromo aldehydes and acetals.529,530 1,2-Dibromoalkyl ethers are obtained from 1-chloroalkyl ethers and bromine, the HC1 formed being finally removed in a vacuum in a stream of C02 CH3CHC10C2H5 + Br2 --------------------- CH2BrCHBrOC2H5 + HC1... 

Violent reaetions have oeeuiTed between ozone and many ehemieals, a small seleetion being aeetylene, alkenes, dialkyl zines, benzene/mbber solution, bromine, earbon monoxide and etliylene, diethyl ether, hydrogen bromide, and nitrogen oxide. 

Bromination of para-alkylated or 2,6-dialkylated phenols and their ethers with Br2 in HF-SbFs leads to the formation of mera-brominated products (Eq. 47) [106]. Sodium or potassium bromide can also be used in place of Br2 in this reaction [107]. 

The actual isolation of beryllium dialkyls in a pure state has only just been accomplished by Gilman and Schulze, and their work throws doubt upon the accurac of that of previous investigators. Their method of procedure is the one suggested by Krause and Wendt. In 1926, Durand claimed to have prepared beryllium methyl iodide, but the work has since been disproved by Gilman and Schulze. These workers have isolated beryllium alkyl halides by heating beryllium, alkyl halides, and ether in the presence of catalysts, such as mercuric chloride, beryllium chloride, or free bromine. The first aryl compound, beryllium phenyl iodide, has been prepared by a similar process. 

Dialkyl 1-formylmethylphosphonates and their enol ethers react with molecular chlorine or bromine at 0 C by an addition-elimination mechanism to give the a-monohalogenated 1-formyl-methylphosphonates in good yields (66-92%). The reaction temperature has to be carefully controlled in order to avoid a second halogenation. 

Because the exploitation of the chemistry of unprotected phosphonylated acetaldehydes is handicapped by the sensitivity of the P-C bond in acidic media, a reliable alternative procedure for the preparation of dialkyl 1-chloro-1-formylmethylphosphonates from dialkyl 2-ethoxy-vinylphosphonates has been developed. Room-temperatme chlorination of 2-ethoxyvinylphosphonates with dry chlorine in CCI4 followed by hydrolysis of the phosphonylated a,p-dichloro ethers with water at 50-60°C gives the expected monochlorinated aldehydes in 73-82% yields (Scheme 5.70). A similar treatment with bromine in water at 0°C converts diisopropyl 2-ethoxyvinylphosphonate smoothly into diisopropyl 1-bromo-1-formylmethylphosphonate in 92% yield. ... 

Brominated dimethyisulphone dialkyl ether Bromine/chlorine containing flame-retardant Blend aromatic bromine, aliphatic chlorine... 

A modified version of this process employs simple alkenes as internal nucleophiles, and the Prins cydization is facilitated by the use of TiBr4 as Lewis acid, which not only activates the aldehyde toward enol ether attack but also delivers a nudeophiUc bromine onto the developing carbocation [8]. Thus, various 2,6-dialkyl-4-bromo-tetrahydropyrans 17 were obtained as single diastereomers within the tetrahydropyran ring and in good yields (Scheme 8.5). 

Applications of Crown Ethers.—Crown ethers have been found to form molecular complexes with bromine that can be used as reagents in bromination reactions, e.g. of alkenes. The crown-halogen interaction seems not to be encapsulation but rather to be the formation of a polymeric structure. The complexes of nitro-nium tetrafluoroborate (NO2BF4) with various crown ethers, for example the 1 1 complex with 18-crown-6, have been reported to be selective nitrating agents. A new rapid synthesis of alkylseleno- and alkyltelluro-arenes from arenediazon-ium tetrafluoroborates and dialkyl diselenides or ditellurides employs KOAc and 18-crown-6 as a phase-transfer catalyst a radical mechanism has been suggested. Fluorine-19 n.m.r. evidence has been presented to show that KF forms... 

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