1- Butanol reaction with hydrogen halides

Elimination of hydrogen bromide from 1,2-dibromo-4-butanol, BrCHjCHBrCHjCHjOH, is accomplished with powdered potassium hydroxide in dry ether. The resulting /3-bromotetrahydrofuran loses another molecule of hydrogen halide when heated with excess powdered base. The over-all yield of dihydrofuran is 62%. This elimination reaction has been extended to the preparation of /3-bromofurans and 2,5-dihydrofurans having two alkyl groups on one of the a-carbon atoms. ... 

Aliphatic or alicyclic fluoroformates may be prepared continuously from the reaction of the corresponding alcohols with a mixture of carbonyl halides e.g. COFj, COCIF and COClj at -20 to +80 "C in the presence of isobutene, which acts as a hydrogen halide acceptor). The process was illustrated using methanol, t-butanol and cyclohexanol as examples [1118]. 

Because the reaction of a secondary or a tertiary alcohol with a hydrogen halide is an SnI reaction, a carbocation is formed as an intermediate. Therefore, we must check for the possibility of a carbocation rearrangement when predicting the product of the substitution reaction. Remember that a carbocation rearrangement will occur if it leads to formation of a more stable carbocation (Section 4.6). For example, the major product of the reaction of 3-methyl-2-butanol with HBr is 2-bromo-2-methylbutane, because a 1,2-hydride shift converts the initially formed secondary carbocation into a more stable tertiary carbocation. 

Different reagents such as HX and PX3 may be used to prepare alkyl halides from primary and secondary alcohols. However, because elimination reactions predominate when tertiary alcohols are treated with phosphorous trihalides, preparing tertiary alkyl halides from tertiary alcohols proceeds with good yields only if concentrated hydrogen halides, HX, are used. The reaction of 2-methyl-2-butanol with hydrochloric acid to produce 2-chloro-2-methylbutane (Eq. 14.17) illustrates this transformation. 

Much of the reactivity of amido ligands involves proton exchange processes that eliminate amine. The exchange is believed to occur by an associative mechanism consequently, the rate of reaction decreases for sterically congested metal complexes. For example, treatment of V[N(CH3)2]j with terf-butanol at room temperature forms V(O-f-Bu) in good yield, while at this temperature the more encumbered complex W[N(CH3)2] reacts only slowly with methanol and ethanol, and not at all with tert-butanoV° The use of bulky N-alkyl substituents allows for the isolation of low-coordinate complexes, such as Cr[N( -Pr)2]3- Amido complexes derived from primary amines can also serve as precursors to imido complexes. In many cases, amido halide complexes form imido complexes by loss of hydrogen chloride in the presence of a base (Equation 4.17). ... 

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