Bromoform, preparation

Methylene bromide (CHjBfj) and methylene iodide (CHjIj) are easily prepared by the reduction of bromoform or iodoform respectively with sodium arsenite in alkaline solution ... 

Note 1. Prepared from cyclooctene, bromoform and KO-tert.-C/jHg (see Ref. 52) or... 

Tribromoacetic acid [75-96-7] (Br CCOOH), mol wt 296.74, C2HBr302, mp 135°C bp 245°C (decomposition), is soluble in water, ethyl alcohol, and diethyl ether. This acid is relatively unstable to hydrolytic conditions and can be decomposed to bromoform in boiling water. Tribromoacetic acid can be prepared by the oxidation of bromal [115-17-3] or perbromoethene [79-28-7] with fuming nitric acid and by treating an aqueous solution of malonic acid with bromine. 

At 225—275°C, bromination of the vapor yields bromochloromethanes CCl Br, CCl2Br2, and CClBr. Chloroform reacts with aluminum bromide to form bromoform, CHBr. Chloroform cannot be direcdy fluorinated with elementary flourine fluoroform, CHF, is produced from chloroform by reaction with hydrogen fluoride in the presence of a metallic fluoride catalyst (8). It is also a coproduct of monochlorodifluoromethane from the HF—CHCl reaction over antimony chlorofluoride. Iodine gives a characteristic purple solution in chloroform but does not react even at the boiling point. Iodoform, CHI, may be produced from chloroform by reaction with ethyl iodide in the presence of aluminum chloride however, this is not the route normally used for its preparation. 

One of the older preparative free-radical reactions is the addition of polyhalomethanes to alkenes. Examples of addition of carbon tetrabromide, carbon tetrachloride, and bromoform have been recorded. The reactions are chain processes that depend on facile abstraction of halogen or hydrogen from the halomethane ... 

The present method utilizes dichlorocarbene generated by the phase-transfer method of Makosza4 and Starks.5 The submitters have routinely realized yields of pure distilled isocyanides in excess of 40%.6 With less sterically hindered primary amines a 1 1 ratio of amine to chloroform gives satisfactory results. Furthermore, by modifying the procedure, methyl and ethyl isocyanides may be prepared directly from the corresponding aqueous amine solutions and bromoform.7 These results are summarized in Table I. 

Prepared by the phase-transfer method using chloroform and aqueous sodium hydroxide with the corresponding amines.8 6 Bromoform substituted for chloroform for ease of fractionation.7... 

Prepared in 80% yields by heating bromoform with mixture of antimony chloride and mercuric chloride... 

Carl Lowig, 1803-1890. Professor of chemistry at Heidelberg, Zurich, and Breslau. He prepared bromine in 1825, but before his investigation was completed Balard had announced the discovery. Lowig discovered bromine hydrate, bromal hydrate, and bromoform, and was the founder of the Silesian chemical industry and of the Goldschmieden alumina works at Deutsch-Lissa. 

The 6,7-dihydro-5/f -1,4-dioxepin (266) has been prepared (54CR(38)982). and more recently it has been shown that the 2,3-dihydro-5jF/-l,4-dioxepins (263) and (265) can be produced from 1,4-dioxine-halocarbene adducts (264), either by heating under reflux in xylene or by treatment with bases. The allylic chlorine atom in (263) is readily substituted by alkoxide or cyanide ions (77ZC331, 76UKZ968). Saturated rings of type (267) have been prepared by the treatment of cyclic acetals of ethane-1,2-diol with vinyl ethers in the presence of boron trifluoride, and l,4-dioxepan-5-one (268) has been prepared by the reaction of bromoform and silver nitrate with aqueous dioxane (60AG415). 

Dibromomethane [74-95-3] (methylene bromide), CH2Br2, is a similar liquid, mp — 52.7° C, bp 96.9°C, Water solubility is 1.17 g/100 g at 15°C. It is prepared by the same methods as bromochloromethane, allowing the reaction to proceed to completion. A laboratory preparation involves removing a bromine from bromoform using sodium arsenite (86). The compound is used as a solvent, as a gauge fluid, and in producing pesticides. Both of these dihalomethanes can be used as dense, readily volatile media for mineral and salt separations. 

Tribromomethane [75-25-2] (bromoform), CHBr3, is usually sold mixed with up to 3—4% ethanol as a stabilizer. The pure liquid has mp, 7.7°C bp, 149.5°C cP A, 2.8912 g/mL 19D 1.5980 (87). Water solubility is about 0.3 g/100 g at 25°C. Bromoform is prepared from chloroform by the replacement procedures indicated (88). The classical method of preparation involves reaction of acetone and sodium hypobromite the latter may be generated from sodium hypochlorite and a bromide (89). Uses have been found in syntheses, in pharmacy as a sedative and antitussive, in gauge fluids, and as a dense liquid for separating minerals. Traces of bromoform and bromochloroforms are likely to be present in municipal waters and wastes as a result of chlorination in the presence of naturally occurring bromide ions and humic substances (90). Removal can be accomplished by adsorption on activated charcoal. 

Dibromocarbene.2 1-Bromobenzocyclobutene can be prepared conveniently by reaction of cycloheptatriene with dibromocarbene generated from bromoform with base in the presence of 18-crown-6. No reaction occurs in the absence of the crown ether. 

Silicobromoform is usually prepared by passing hydrogen bromide over heated silicon112,4,5 or a silicide such as copper silicide.3 The product, consisting of a mixture of silicon tetrabromide with a few per cent of tri- and dibromosilanes, is purified by shaking with mercury, if necessary, to remove any free bromine, and by fractional distillation. The use of metal silicides instead of silicon does not add appreciably to the yield of the bromoform and is not recommended in the following procedure. 

Iodoform from Ethyl Alcohol.—Chloroform and bromoform cannot be prepared electrolytically from alcohol (Elbs and Herz4). This is contrary to the claims of the I). R. P. No. 

Coughlin 1 has. substantially verified the results of Elbs in the case of bromoform. He obtained only small quantities of this body which can be easily prepared electro-lytically from acetone. The formation of iodoform, on the contrary, takes place smoothly. It is obtained technically according to the above-mentioned patent. Elbs and Herz have established the following conditions for this reaction. 

In recent years, Seebach et al. have elaborated synthetic applications of ot-halo-lithiocyclopropanes, for instance, insertion of a CO-group between the two vinylic carbon atoms of an olefin (Eq. (43) 48)), annulations of four-membered rings and of lactones (Eq. (44) 9y), preparation of cyclopropylketones from olefins (Eq. (45) 49>), and, by using the same cyclopropylbromohydrins, bromovinylations S0) and synthesis of methyleneeyclopropanes from olefins, bromoform and aldehydes (Eq. (46)51)). 

Hill et al. [61] have reported on the feasibility to use carbon nanotubes as eleetrode material, by paeking oxidized CNTs into a glass capillary in bromoform, nujol, deionised water or mineral oil. When neeessary, bromoform was eliminated by baeking the packed nanotubes in an oven at 80-100 °C. Britto and co-workers [62] have proposed the preparation of an eleetrode based on the dispersion of CNTs with bromoform and packing inside a glass tube. 

When each stereoisomeric reactant forms a different stereoisomeric product the reaction is known as stereospecific reaction. For example, the addition of CBr2 (dibromo-carbene, prepared from bromoform and base) to ds-2-butene gives cis-2,3-dimethyl-l,l-dibromocyclopropane (1.32), whereas addition of CBr2 to the trans-isomer exclusively yields the trans-cyclopropane 1.33. 

The method of preparation of the above silver(I) compounds is identical to that used in Sec. A. The compounds can be purified in an identical manner except that a chloroform-cyclohexane mixture is used. The compounds are obtained in approximately 40% yields. Anal. Calcd. for AgCisHisOsFeCcyclo-octene complex) C, 36.72 H, 3.56 mol. wt., 425. Found C, 36.1 H, 3.47 mol. wt., 425 (bromoform). Satisfactory carbon and hydrogen analyses were not obtainable for the remainder of the compounds, since they lose olefin readily. ... 

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