2- Butanol from 2-bromobutane

Use a descriptive title for your experiment. n-Butyl Bromide. So what Did you drink it Set it on fire What The Synthesis of 1-Bromobutane from 1 -Butanol—now that s a title. 

Tundo, P. and Selva, M. (2005). Continuous-flow, gas phase synthesis of 1-chlorobutane (1-bromobutane) from 1-butanol and aqueous HCl (HBr) over silica-supported quaternary phosphonium salt. Green Chem., 7,464-467. 

Bromobutane can be obtained in one step from each of the following precursors butane, 2-butanol, 1-butene, and 2-butene. Write an equation for each method. Describe the advantages or disadvantages of each. 

The essential feature of the 8 2 mechanism is that the reaction takes place in a single step without intermediates when the incoming nucleophile attacks the alkyl halide or tosylate (the substrate) from a direction directly opposite the group that leaves. As the nucleophile comes in on one side of the substrate and bonds to the carbon, the halide or tosylate departs from the other side, thereby inverting the stereochemical configuration. The process is shown in Figure 11.3 for the reaction of (S)-2-bromobutane with HO , leading to (/2)-2-butanol. 

When a reactant is chiral but optically inactive because it is racemic, any products derived from its reactions with optically inactive reagents will be optically inactive. For example, 2-butanol is chiral and may be converted with hydrogen bromide to 2-bromobutane, which is also chiral. If racemic 2-butanol is used, each enantiomer will react at the same rate with the achiral reagent. Whatever happens to (7 )-( )-2-butanol is mirrored in a corresponding reaction of (5)-(-b)-2-butanol, and a racemic, optically inactive product results. 

ANSWER Retrosynthetic disconnection of 5-nonanone suggests butylmagnesium bromide and pentanenitrile as immediate precursors. Butylmagnesium bromide can, in turn, be synthesized from 1-bromobutane. Pentanenitrile can also be synthesized from 1-bromobutane, via Siyf2 reaction of 1-bromobutane with cyanide. To begin the synthesis, 1-bromobutane can be prepared from 1-butanol by reaction with phosphorus tribromide. 

Consider the mechanistic step in the conversion of 1-butanol to 1-bromobutane in which bromide ion displaces water from the oxonium ion 1 (Eq. 14.10). a. What evidence, if any, is there that this step involves backside attack by the nucleophile ... 

This model for the transition state is based on experimental evidence. When (f )-2-bromobutane reacts with sodium hydroxide, the substitution product is (5)-2-butanol. The reaction therefore occurs with inversion of configuration. This result indicates that the nucleophile approaches the electrophilic carbon atom from the back side—that is, from the side direcdy opposite the leaving group. The leaving group departs simultaneously from the opposite side of the substrate. 

In the second step of the reaction, the C—O bond of the phosphite ester breaks, with predominant inversion of configuration. Some loss of optical activity and a smah amount of rearrangement may occur. For example, 2-bromobutane formed from opticahy active 2-butanol is about 80% optically pure. About 2% of the product is 2-bromo-2-methylpropane. 

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