Dibromides protection

Generally, the successful conversion of 20-ketopregnanes to 17-hydroxy-androstanes with peracids requires the protection of other ketones, with the exception of those at C-11, and possibly C-12 e.g., as ketals or cyanohydrins ) and isolated double bonds e.g., as dibromides). Unprotected hydroxyl groups do not interfere, except, as expected, a 17a-hydroxy-20-keto steroid is oxidized to the 17-ketone. The use of nitrate esters to protect... 

A second, more convenient approach was tried starting with dicyclopropyla-cetylene 56 [15-17] which, after deprotonation with tert-butyllithium at both propargylic positions, yielded the bisaldehyde 57 upon treatment with dimethyl-formamide. The latter was converted to the bis(dibromoethenyl) derivative 58, and this in turn to the dibromotriyne 59 by standard methods (Scheme 11) [18]. The dibromide 59 was coupled with the ethynylcyclopropylheterocuprate 50 to give the terminally bis-protected pentayne 60. 

Grain and foodstuffs are constantly attacked by weevils. Fumigation with carbon bisulfide, methyl bromide, and Chlorosol fumigant (a carbon tetrachloride-ethylene dibromide mixture) provides effective control where storage areas are built to handle these materials. Such storage equipment is limited, so there is need for an insecticide with low mammalian toxicity in order to achieve continuous protection by direct application. 

Vaughan-Dellarco VL, Fowle JR, Rosenthal S. 1985. Assessment of the mutagenic potential of carbon disulfide, carbon tetrachloride, dichloromethane, ethylene dichloride, and methyl bromide A comparative analysis in relation to ethylene dibromide. Washington, DC U.S. Environmental Protection Agency, Office of Health and Environmental Assessment. EPA/600/6- 85/001. 

This Statement was prepared to give you information about 1, 2-dibromoethane (ethylene dibromide, EDB) and to emphasize the human health effects that may result from exposure to it. The Environmental Protection Agency (EPA) has identified 1,177 sites on its National Priorities List (NPL). 1,2-Dibromoethane has been found at 9 of these sites. However, we do not know how many of the 1,177 NPL sites have been evaluated for 1,2-dibromo-ethane. As EPA evaluates more sites, the number of sites at which 1,2-dibromoethane is found may change. The information is important to you because 1,2-dibromoethane may cause harmful health effects and because these sites are potential or actual sources of human exposure to 1,2-dibromoethane. 

EPA. 1983. Ethylene dibromide (EDB). Washington, DC US Environmental Protection Agency, Office of Pesticide Programs. Position Doc 4... 

EPA. 1985. Drinking water criteria document for ethylene dibromide (EDB) (Draft). Cincinnati, OFI US Environmental Protection Agency, Environmental Criteria and Assessment Office. EPA-600/X-84/181. NTIS no. PB86-118247... 

EPA. 1989c. Final Draft of the Drinking Water Criteria Document for Ethylene Dibromide. Washington, D.C. US Environmental Protection Agency, Office of Drinking Water. 

Short RD, Minor JL, Winston JM, et al. 1977. Task IV. Developmental toxicity of ethylene dibromide inhaled by rats and mice during organogenesis. Toxicity studies of selected chemicals. Washington, D C. US Environmental Protection Agency, Office of Toxic Substances. EPA-560/6-77-028. NTIS no. PB-273 267, 1-15 117-127. 

Strained alkenes, including cyclobutenes 29 [120] and benzcyclobutadiene derivatives 30 [121], can be prepared by this route. Particularly advantageous is the wide range of reduction potentials for 1,2-dibromides, which allows some selective reactions. The dibromide 26 can be purified from any of the isomer 25 by reduction at -0.86 V vs. see when the diequatorial bromide remains unchanged and the diaxial compound is converted to the alkene [110], Bromination of dialkenes followed by selective debromination to recover one alkene leads to protection of the other alkene as the dibromide. Subsequently the second alkene can be recovered by reduction at more negative potentials [122],... 

Short RD Jr, Minor JL, Ferguson B, et al Toxicity Studies of Selected Chemicals, Task I— The Developmental Toxicity of Ethylene Dibromide Inhaled by Rats and Mice During Organogenesis. Report No EPA-560/6-76-018. Washington, DC, US Environmental Protection Agency, Office of Toxic Substances, 1976... 

Aza-2-benzoylbicyclo[3.3.1]nonan-8-one (217) has been used for the S3mthe-sis of isomeric thiazolo[4,5-c]azocine 221 (83CPB2094). Bromination of 217 in the a-position by pyridinium dibromide hydrobromide and condensation of bromoketone 218 with thiourea leads to aminothiazoloazocine 219. Successive deamination of 219, the removal of N-benzoyl protection and methylation gives the target azocine 221 (Scheme 61). 

These agents would be used as adjuncts to beta lactams since they have no antibacterial activity in their own right. A key reaction in the synthesis of each compound involves the replacement of the amine at 6 and the protection of that position as a mono- or di-halide. Thus reaction of 6-APA (2-4) with nitrous acid gives the diazonium salt (9-1) this is converted to the dibromide (9-2) on treatment with bromine. The ring sulfur is then oxidized with permanganate to the sulfone (9-3). Hydrogenolysis of the product replaces the two bromine atoms by hydrogen to afford sulbactam (9-4) [13]. 

Caution o-Xylylene dibromide is a powerful and persistent lachrymator. The preparation and all subsequent handling of this substance should, therefore, be carried out in an efficient hood with adequate protection by rubber gloves. A gas mask should be at hand for emergency. All apparatus coming in contact with the dibromide should be immersed in alcoholic alkali contained in a large crock with a lid. A period of 24 hours is sufficient for decontamination. Waste substances stick as filter paper and corks usually require several days of such soaking before they can be safely discarded. 

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