Reagents for Interconverting Carboxylic Acids and Acid Derivatives

ETHERS Classification of Ethers:   Symmetrical ethers – two groups attached to O are identical Ex. CH3CH2OCH2CH3 – diethyl ether  Unsymmetrical ethers – two groups attached to O are not identical Ex. CH3CH2OCH3 – ethyl methyl ether Physical Properties of Ethers:   Ethers have much lower boiling points compared to alcohols of comparable MWs.  BPs of ethers increases with increasing MW.  BPs of isomeric ethers increase with increasing alkyl chain length.  BPs of ethers are about the same as those of alkanes of comparable MWs.  Solubility of ethers in water is comparable to that of alcohols.  As chain length of ethers increases, solubility in water decreases.  Branching of the alkyl chain results in greater solubility since London forces are weaker.
 O 111o

 H3C

 CH3

  The C-O bonds in ethers are polar, with O being - and each of the C atoms bearing a +.  The C-O-C bond angle is 111o, slightly higher than the H-O-H bond angle in water because of the stronger electron repulsion between the bulky alkyl groups.

Preparation of Ethers: 1. Preparation of symmetrical ethers from alcohols H2SO4 R O R + H2O 2ROH  2. Williamson Ether Synthesis

R O Na
-

-

+ +

+

R'X

R O R' + NaX

   

Ar O Na + RX Ar O R + NaX Involves a nucleophilic substitution reaction. Halide ion is displaced by the alkoxide or phenoxide ion. Gives best results when 1o alkyl halides are used. Mechanism is SN2.

 Alkoxides may be prepared by reacting an alcohol with NaH or by reacting an alcohol with Na metal.  Phenoxides may be prepared by reaction of phenols with NaOH

ROH + NaH ROH + Na ArOH + NaOH

RO Na
-

-

+

+

H2

RO Na

+

+ 1/2 H2
+

ArO Na

-

+ H2O

 When 3o alkyl halides are reacted with alkoxide or phenoxide ions, elimination is the major reaction, not substitution  When 2o alkyl halides are used, yield of ether is lower since elimination is a competing reaction.  Use 1o alkyl