Mastering Chemistry Help

Test to distinguish primary, secondary and tertiary alcohol Oxidation of alcohols involves the formation of a carbon oxygen double bond with the cleavage of an O-H and C-H bonds. The products of oxidizing reaction depends on the nature of alcohols (primary, secondary or tertiary nature of the carbon) and also the oxidizing agent used. Hence this reaction can be utilized for distinguishing the primary, secondary and tertiary alcohols from one another A primary alcohol when treated with potassium to an aldehyde and then to an acid. Both the aldehyde and acid contain the same number of carbon atoms as the parent alcohol. A secondary alcohol on oxidation with acidified K2Cr2O7 or chromium trioxide (CrO3) forms a ketone with the same number of carbon atoms as the parent alcohol. The ketone is further oxidized under strong conditions to form a mixture of acids, each containing lesser number of carbon atoms than the parent alcohol. Tertiary alcohols do not undergo oxidatio...

Alcohols undergo dehydration (removal of a molecule of water) on treating them with protonic acids(conc. H 2 SO 4 or H 3 PO 4 ) or catalysts such as anhydrous zinc chloride or alumina to form alkenes. Ethanol undergoes dehydration to form ethylene by heating it with concentrated H 2 SO 4 at 443 K. C 2 H5OH (ethanol)----(conc.H 2 SO 4 , 443 K)-----> CH 2 = CH 2 (ethylene) + H 2 O Secondary and tertiary alcohols are dehydrated under milder conditions. For example The relative ease of dehydration of alcohols follows the order: Tertiary alcohol > Secondary alcohol > Primary alcohol In the above reaction, if alcohol is in excess acidic dehydration takes place in a different way to yield an ether. The ether is formed by the elimination of one water between molecule from two hydroxyl groups.  Related post Chemical properties of Alcohols and Phenols

Reaction with phosphorus halides and SOCl 2 Alcohols react with phosphorus tri or penta halides or thionyl chloride in pyridine to form the corresponding alkyl halides. 3R - OH + PX 3 --------------> 3R - X + H 3 PO 3 R - OH + PX 5 --------------> R - X + POX 3 + HX R - OH + SOCl 2 -------(pyridine)---------> R - Cl + SO 2 + HCl Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide 3ROH + PBr 3 ---------------> 2RBr + H 3 PO 3 Alkyl iodides are obtained by reacting and alcohol with PI 3 3ROH + PI 3 -------(red p + I 2 )-------> 3RI + H 3 PO 3 3C 2 H 5 OH + PI 3 -------(red p + I 2 )-------> 3C 2 H 5 OH + H 3 PO 3 PBr and PI 3 are obtained in the reaction mixture by the action of red phosphorous and bromine or iodine. Alkyl chlorides are prepared by reacting an alcohol with phosphorus trichloride, phosphorus penta chloride or thionyl chloride. 3R - OH + PCl 3 ----------------> 3R - Cl + H 3 PO 3 3C 2 H 5 ...

Alcohols react with hydrogen halides to give alkylhalides. ROH + HX --------> R-X + H2O The alcohol may be primary, secondary or tertiary and hydrogen halide may be HCl, HBr or HI. For example, CH 3 CH 2 CH 2 OH + HI ------------> CH 3 CH 2 CH 2 I + H 2 O To increase the yield of haloalkane a dehydrating agent like anhydrous ZnCl2 is used to remove the water formed. In this reaction, the reactivity of alcohols decreases in the order tertiary > secondary > primary. Among hydrogen halides reactivity decreases in the order HI > HBr > HCl  Related post Chemical properties of Alcohols and Phenols