Reaction of Alcohols with Hydrogen Halides ROH+ HX-→RX+HOH Hydrogen halide reactivity HI HBr HCI HF most reactive least reactive Alcohol reactivity H H R H一C一OH <R一COH <R-C-OH <R一C-OH H H R R Methyl 20 3° Less Reactivity More reactive reactive
Reaction of Alcohols with Hydrogen Halides ROH + H X R X + HOH Hydrogen halide reactivity HI HBr HCl HF most reactive least reactive Alcohol reactivity
Examples SOC CH3CH(CH2)sCH3 2 K2C03 CH3CH(CH2)5CH3 OH cl (81%) (pyridine often used instead of K2CO3) PBr3 (CH3)2CHCH2OH (CH3)2CHCH2Br (55-60%)
CH3CH(CH2)5CH3 OH SOCl2 K2CO3 CH3CH(CH2)5CH3 Cl (81%) (pyridine often used instead of K2CO3) (CH3)2CHCH2OH (55-60%) (CH3)2CHCH2Br PBr3 Examples
Preparation of Alkyl Halides (CH3)3COH HCI 25°C(CHg)3CCI+H20 78-88% 80-100°C OH HBr Br+H2O 73% 120°C CH3(CH2)5CH2OH HBr CH3(CH2)5CH2Br +H20 87-90%
Preparation of Alkyl Halides (CH 3 ) 3COH + HCl (CH 3 ) 3CCl + H 2 O 78-88% + H 2 O 73% CH 3(CH 2 ) 5CH 2OH + HBr CH 3(CH 2 ) 5CH 2Br + H 2 O 87-90% 25 ° C 80-100 ° C 120 ° C OH + HBr Br
Preparation of Alkyl Halides A mixture of sodium bromide and sulfuric acid may be used in place of HBr. NaBr H2SO4 CH:CH2CH2CH2OH CH3CH2CH2CH2Br heat 70-83% 120°C CH3(CH2)sCH2OH HBr CH3(CH2)5CH2Br H2O 87-90%
Preparation of Alkyl Halides CH 3CH 2CH 2CH 2OH CH 3CH 2CH 2CH 2Br NaBr H 2SO 4 70-83% heat A mixture of sodium bromide and sulfuric acid may be used in place of HBr. CH 3(CH 2 ) 5CH 2OH + HBr CH 3(CH 2 ) 5CH 2Br + H 2 O 87-90% 120 ° C
4. Diazonium coupling (for aryl halide only） Formation of a diazonium salt conc.HNO3 NO2 HCI/Sn NH2 conc.H2SO NH2 HNO2 (or HCI+NaNO2) 三N (diazonium salt) <5c NH2 HNO2 OH (or HCI NaNO2) >5℃ From diazonium salt,you can make the following aryl halide:
conc. HNO3 conc. H2SO4 NO2 HCl / Sn NH2 NH2 HNO2 (or HCl + NaNO2) < 5 Co N N + (diazonium salt) NH2 HNO2 (or HCl + NaNO2) > 5 Co OH From diazonium salt, you can make the following aryl halide: 4. Diazonium coupling (for aryl halide only) Formation of a diazonium salt