• Reactions of glycols

(1) Oxidation

(a) With acidified $KMnO_4$ , $1^o$ & $2^o$ $\rightarrow$ acid or $3^o$ $\rightarrow$ ketone

• Fission or cleavage of C-C bond takes place

$R_2-C-OH+R^1-CH-OH$ $R_2-C-OH+R^1-CH-OH \rightarrow R_2C=O+R^1COOH$ $R_2C=O$

(b) with periodic acid ($HIO_4$ or $NaIO_4$ (sodium periodate)

• $1^o$ , $2^o$ aldehydes or Ketones $3^o$

• $2CH_2OH+HIO_4/NaIO_4 \rightarrow 2HCHO+H_2O+HIO_3/NaIO_3$

• $R-CHOH-CH_2OH \xrightarrow {HIO_4} RCHO+HCHO+H_2O+HIO_3$

• $R_2-COH-CH_2OH \xrightarrow {HIO_4} R_2C=O+HCHO+H_2O+HIO_3$

7. cis-glycols $\xrightarrow {HIO_4}$ trans-glycols $\xrightarrow {HIO_4}$

$(CH_3)_2-\underset{\underset{OH}{|}}{C}-\underset{\underset{OH}{|}}{C}-(CH_3)_2$

• R.D.S. $\rightarrow$ formation of cyclic intermediates

• Pinacol $\xrightarrow [{RDS slow}]{HIO_4}$ cyclic intermediate $\xrightarrow{fast}$ aldehyde / ketone

• (c) with lead tetraacetate $(CH_3COO)_4 Pb/CH_3COOH$

• Glycol which have low solubility in aq medium

• $HIO_4 \rightarrow$ aq medium is used

• $Pb(OAC)_4 \rightarrow$ organic solvent benzene, toluene, DCM, THF cis & trans 1,2-diols cis-> trans-

• $2CH_2OH \xrightarrow [{(CH_3COO)_4Pb}]{glacial \hspace{1mm} acetic\hspace{1mm} acid} HCHO+HCHO+Pb(OOCCH_3)_2+2CH_3COOH$

$2(CH_3)_2-C-OH \rightarrow 2(CH_3)_2-C=O$

(10) Pinacole - pinacolone rearrangement

Rearrangement of a pinacal (1, 2-test-diol) to a ketone in presence of conc $H_2SO_4$ or anhydrous $ZnCl_2$

• R = $CH_3$, $C_6H_5$ $\rightarrow$ symmetrical

• R = H, $CH_3$, Ph $\hspace{3mm}$ H > Ph > $Me_3$ > C > $MeCH_2$ > Me

migratory aptitude $\hspace{3mm}$ H > Ar > R

(ⅰ) Nature of group(electron rich group migrates)

(iii) Stability of cyclic intermediate

• I more stable II

• Ph gp. migration is preferred