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RCH=CH 2 + HBr → RCHBrCH 3. Under free radical conditions, the direction of the addition can be reversed. Free-radical addition is used commercially for the synthesis of 1-bromoalkanes, precursors to tertiary amines and quaternary ammonium salts. 2-Phenethyl bromide (C 6 H 5 CH 2 CH 2 Br) is produced via this route from styrene.
Prior to the introduction of this chromium-based protocol, olefination reactions generally gave Z alkenes or mixtures of isomers. [1] Similar olefination reactions had been performed using a variety of reagents such as zinc and lead chloride; [5] however, these olefination reactions often lead to the formation of diols—the McMurry reaction—rather than the methylenation or alkylidenation of ...
Most 1-bromoalkanes are prepared by free-radical addition of hydrogen bromide to the 1-alkene, which is 1-pentene in the case of 1-bromopentane. These conditions lead to anti-Markovnikov addition, giving the 1-bromo derivative. [2] It is also formed by the reaction of 1-pentanol with hydrogen bromide.
2-Bromohexane is the organobromine compound with the formula CH 3 CH(Br)(CH 2) 3 CH 3. It is a colorless liquid. The compound is chiral. Most 2-bromoalkanes are prepared by addition of hydrogen bromide to the 1-alkene. Markovnikov addition proceeds in the absence of free-radicals, i.e. give the 2-bromo derivatives. [2]
Straight-chain terminal alkenes, also called linear alpha olefins (LAO) or normal alpha olefins (NAO), are alkenes (olefins) having a chemical formula C n H 2n, distinguished from other alkenes with a similar molecular formula by being terminal alkenes, in which the double bond occurs at the alpha (α-, 1-or primary) position, and by having a linear (unbranched) hydrocarbon chain.
H 2 C=CH 2 + HBr → H 3 C-CH 2 Br. Bromoethane is inexpensive and would rarely be prepared in the laboratory. A laboratory synthesis includes reacting ethanol with a mixture of hydrobromic and sulfuric acids. An alternate route involves refluxing ethanol with phosphorus and bromine; phosphorus tribromide is generated in situ. [4]
Selenic acid is liberated in the final step to give the 1,2-dicarbonyl product. Allylic oxidation using selenium-dioxide proceeds via an ene reaction at the electrophilic selenium center. A 2,3-sigmatropic shift , proceeding through an envelope-like transition state , gives the allylselenite ester, which upon hydrolysis gives the allylic alcohol.