15.2 Preparation of Alcohols by Reduction of Aldehydes and Ketones TABLE 15.1 Summary of Reactions Discussed in Earlier Chapters That Yield Alcohols( Continued) Reaction(section) and comments General equation and specific example Reaction of Grignard reagents with ary alcohols in which two of the sub- 2RMgX+ R' COR"1. diethyl ethe rCoh+R"OH esters(Section 14.10) Produces teri stituents on the hydroxyl-bearing carbon are derived from the Gr 2CH3 CH2 CH2 CH2 CH2 MgBr CH3 CH diethyl ether 2.H2O Pentylmagnesium CH3CCH2 CH2 CH2CH2 CH3 CH2 CH2 CH2CH2 CH3 6-Methyl-6-undecanol (75%) importance of alcohols in synthetic organic chemistry. Some of these methods involve Recall from Section 2.16that reduction of carbonyl groups ecrease in the nu OH bonds between car oxygen educing agent number of bond arbon and hydrogen(or We will begin with the reduction of aldehydes and ketones 15.2 PREPARATION OF ALCOHOLS BY REDUCTION OF ALDEHYDES AND KETONES The most obvious way to reduce an aldehyde or a ketone to an alcohol is by hydro- genation of the carbon-oxygen double bond. Like the hydrogenation of alkenes, the reac tion is exothermic but exceedingly slow in the absence of a catalyst. Finely divided met als such as platinum, palladium, nickel, and ruthenium are effective catalysts for the hydrogenation of aldehydes and ketones. Aldehydes yield primary alcohols RCH+ RCHOH Aldehyde Hydrogen Primary alcoho CHO CH -->CH3O- CHOH p-Methoxybenzaldehyde Methoxybenzyl alcohol (92 Back Forward Main MenuToc Study Guide ToC Student o MHHE Websiteimportance of alcohols in synthetic organic chemistry. Some of these methods involve reduction of carbonyl groups: We will begin with the reduction of aldehydes and ketones. 15.2 PREPARATION OF ALCOHOLS BY REDUCTION OF ALDEHYDES AND KETONES The most obvious way to reduce an aldehyde or a ketone to an alcohol is by hydro￾genation of the carbon–oxygen double bond. Like the hydrogenation of alkenes, the reac￾tion is exothermic but exceedingly slow in the absence of a catalyst. Finely divided met￾als such as platinum, palladium, nickel, and ruthenium are effective catalysts for the hydrogenation of aldehydes and ketones. Aldehydes yield primary alcohols: RCH O Aldehyde H2 Hydrogen Pt, Pd, Ni, or Ru RCH2OH Primary alcohol H2, Pt ethanol CH3O CH O p-Methoxybenzaldehyde CH3O CH2OH p-Methoxybenzyl alcohol (92%) reducing agent C O C H OH 15.2 Preparation of Alcohols by Reduction of Aldehydes and Ketones 583 TABLE 15.1 Summary of Reactions Discussed in Earlier Chapters That Yield Alcohols (Continued) Reaction (section) and comments General equation and specific example Reaction of Grignard reagents with esters (Section 14.10) Produces terti￾ary alcohols in which two of the sub￾stituents on the hydroxyl-bearing carbon are derived from the Grignard reagent. RCOR O X 2RMgX RCOH ROH W W R R 1. diethyl ether 2. H3O Ethyl acetate CH3COCH2CH3 O X Pentylmagnesium bromide 2CH3CH2CH2CH2CH2MgBr 1. diethyl ether 2. H3O 6-Methyl-6-undecanol (75%) CH3CCH2CH2CH2CH2CH3 W W OH CH2CH2CH2CH2CH3 Recall from Section 2.16 that reduction corresponds to a decrease in the number of bonds between carbon and oxygen or an increase in the number of bonds between carbon and hydrogen (or both). Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website