Bromopentane

Bromopentane. Proceed as for n-Amyl Bromide, but use 88 g. (108 ml.) of methyl n-propyl carbinol (2-pentanol), b.p. 118-5°. During the washing with concentrated hydrochloric acid, difficulty may be experienced in separating the acid layer this is overcome by adding a little water to decrease the density of the acid. Distil the purified product through a fractionating colunm some amylene passes over first, followed by the 2-bromopentane at 115-118° (120 g.). 

A carbon with four different groups attached to it is a chi rality center (a) In 2 bromopentane C 2 satisfies this requirement (b) None of the carbons in 3 bromopentane has four different substituents and so none of its atoms IS a chirality center... 

Synthesize 2-bromopentane from acetylene and any alkyl halide needed. More than one step is required. 

A complication of such reactions is competition from elimination reactions rather than substitution (see Section 18.5). (a) Predict the possible products from the reaction of 2-bromopentane with sodium hydroxide, (b) What can be done to favor the... 

The elimination of hydrogen halides from some monohaloalkanes can result in the formation of two alkenes. Consider 2-bromopentane, for example. You can see from its structure that the elimination of HBr will produce both pent-l-ene and pent-2-ene. 

If there is possibility of formation of more than one alkene due to the availability of more than one 3-hydrogen atoms, usually one alkene is formed as the major produet. These form part of a pattern first observed by Russian ehemlst, Alexander Zaitsev (also pronounced as Saytzeff) who In 1875 formulated a rule which can be summarised as in dehydrohalogenation reactions, the preferred product is that alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms. Thus, 2-bromopentane gives pent-2-ene as the major product. 

One further consideration relating to the nature of about the double bond. For instance, base-catalysed the products in eliminations is the stereochemistry elimination of HBr from 2-bromopentane gives three... 

Thiopental Thiopental, 5-ethyl-5-(l-methylbutyl)2-thiobarbituric acid (1.2.10), is synthesized by the alkylation of ethyhnalonic ester with 2-bromopentane in the presence of sodium ethoxide. The product ethyl-(l-methylbutyl)malonic ester (1.2.9) undergoes hete-rocyclization with thiourea, using sodium ethoxide as a base [16,17]. 

Problem 7.33 Explain the fact that whereas 2-bromopentane undergoes dehydrohalogenation with C2H3O K to give mainly 2-pentene (the Sayzteff product), with MCjCO K it gives mainly 1-pentene (the anti-Sayzteff, Hofmann, product). 

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