Bromine with silanes

Bromine reacts very violently at ambient temperature with silane (SiH4). This reaction leads to detonations. One needs to use temperatures which do not exceed -30°C to carry out this reaction safely. Note that the same dangers were observed with germanium (GeH4). 

Although we will deal with organic radicals in solution, it is worth mentioning that the reactivity of atoms and small organic radicals with silanes in the gas phase has been studied extensively. For example, the bond dissociation energies of a variety of Si-H bonds are based on the reaction of iodine or bromine with the corresponding silanes.1... 

This product is then treated with acryloyl chloride. The initial step in this case probably involves the acylation of nitrogen on the enamine conjugate addition then completes the formation of the lactam ring (23-5). Treatment of that product with triethyl silane then reduces the ring unsaturation and cleaves the benzylic nitrogen bond on the auxiliary to yield (23-6) as the optically pure tmns isomer. Displacement of bromine with the mercapto benzthiazole (23-7) completes the synthesis of izonsteride (23-8) [25]. 

Metal Azides. Vapor with silver or sodium azide forms explosive bromine azide.10 Metals. Impact-sensitive mixtures are formed from lithium or sodium in dry bromine.11 Potassium, germanium, antimony, and rubidium ignite in bromine vapor.12 Violent reaction occurs with aluminum, mercury, or titanium.13 Methanol. Vigorously exothermic reaction on mixing the liquids.14 Nonmetal Hydrides. At room temperature, violent explosion and ignition occur with silane and its homologs15,16 and with germane.17... 

Formation of 2-Trimethylsilylaziridines. The photochemical or thermal reaction of vinyltrimethylsilane with ethyl azido-formate or phenyl azide provides the trimethylsilylaziridine in modest yields (eq 22). Reduction of the formyl amide gives the parent trimethylsilylaziridine (eq 23). Trimethylsilylaziridines were also formed from the reaction of a-lithiochloromethyltri-methylsilane with imines, but this reaction only works with the imines of aldehydes. The reaction of bromotriazide, formed in situ from the reaction of bromine with sodium azide, with vinyl-silanes forms silylaziridines as well. This reaction was not carried out with vinyltrimethylsilane. However, vinyltriphenylsilane gave a 50% yield of 2-triphenylsilylaziridine under these conditions. 

Halogens, Hydrogen Halides, and Other Covalent Halides. Most compounds containing Si—H bonds react very rapidly with the free halogens. An explosive reaction takes place when chlorine or bromine is allowed to react with SiH at room temperature, presumably forming halogenated silane derivatives (3). At lower temperatures, the reactions are moderated considerably, for example. 

The six-position may be functionalized by electrophilic aromatic substitution. Either bromination (Br2/CH2Cl2/-5°) acetylation (acetyl chloride, aluminum chloride, nitrobenzene) " or chloromethylation (chloromethyl methyl ether, stannic chloride, -60°) " affords the 6,6 -disubstituted product. It should also be noted that treatment of the acetyl derivative with KOBr in THF affords the carboxylic acid in 84% yield. The brominated crown may then be metallated (n-BuLi) and treated with an electrophile to form a chain-extender. To this end, Cram has utilized both ethylene oxide " and dichlorodimethyl-silane in the conversion of bis-binaphthyl crowns into polymer-bound resolving agents. The acetylation/oxidation sequence is illustrated in Eq. (3.54). 

Silane radical atom transfer (SRAA) was demonstrated as an efficient, metal-free method to generate polystyrene of controllable molecular weight and low polydispersity index values. (TMSlsSi radicals were generated in situ by reaction of (TMSlsSiH with thermally generated f-BuO radicals as depicted in Scheme 14. (TMSlsSi radicals in the presence of polystyrene bromide (PS -Br), effectively abstract the bromine from the chain terminus and generate macroradicals that undergo coupling reactions (Reaction 70). 

Silicon, like carbon, is relatively inactive at ordinary temperatures. But, when heated, it reacts vigorously with the halogens (fluorine, chlorine, bromine, cmd iodine) to form halides and with certain metals to form silicides. It is unaffected by all acids except hydrofluoric. At red heat, silicon is attacked by water vapor or by oxygen, forming a surface layer of silicon dioxide. When silicon and carbon are combined at electric furnace temperatures of 2,000 to 2,600 °C (3,600 to 4700 °F), they form silicon carbide (Carborundum = SiC), which is an Importeint abrasive. When reacted with hydrogen, silicon forms a series of hydrides, the silanes. Silicon also forms a series of organic silicon compounds called silicones, when reacted with various organic compounds. 

Interaction of silane and its homologues with bromine at ambient temperature is explosively violent [1] and temperatures of below -30°C are necessary to avoid ignition of the reactants [2], Ignition of disilane at -95°C and of germane at -112°C emphasises the need for good mixing to dissipate the large exotherm [3], Phosphine reacts violently with bromine at ambient temperature [4],... 

MRH Bromine 1.21/91, carbon tetrachloride 2.89/83, chlorine 3.85/82 Silane burns in contact with bromine, chlorine or covalent chlorides (carbonyl chloride, antimony pentachloride, tin(IV) chloride, etc.) [1], Extreme caution is necessary when handling silane in systems with halogenated compounds, as a trace of free halogen may cause violent explosions [2],... 

Reaction of silanes with chlorine or bromine is violent. 

The 3-thienyl substituted silane 30 was trilithiated by Nakayama and coworkers, when reacted with a three-fold excess of n-butyllithium (Scheme 11). Target molecule 31 can also be obtained by bromine-lithium exchange, but with a reduced yield. 

The most direct procedure for the synthesis of a-haloacyl silanes is electrophilic halo-genation of enolates or enol ethers of acyl silanes. This has been achieved with the silyl enol ethers using bromine at low temperatures, but the reaction suffers from the general... 

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