Question

A mixture of an acid anhydride (A) and a monobasic acid (B) on heating produces another monobasic acid (C) of equivalent weight 74 and an anhydride (D). The acids and anhydrides remain in equilibrium. The anhydride (D) contains two identical flouro alkyls groups. The acid (B) contains a trifluoro methyl group and has an equivalent weight of 128. Give the structures of (A) to D) with proper reasoning (Atomic weight of fluorine 19).

Answer 1

Acid anhydride (A) +`underset((CF_(3) "group")) ("Monobasic acid (B)")` `hArr`Monobasic acid(C ) +`underset((Two CF_(3) "group")) ("Anhydride(D)")`
Eq. wt.=128 Eq. wt.=74
Probable formula of acid (B)=`CF_(3)(CH_(2))_(n)COOH`
Equivalent weight of (B) =`("Molecular weight")/("Basicity")`
`128=(57+12+14n+12+32+1)/1`
n=1
`therefore(B)=CF_(3)CH_(2)COOH` and `(D)=(CF_(3)CH_(2)CO)_(2)O`
Similarly, molecular formula of acid (C ) can be calculated to be `CH_(3)CH_(2)COOH`. The reaction, therefore, can be given as,
`underset((A))((CH_(3)CH_(2)CO)_(2)O)+underset((B))(F_(3)"CC"H_(2)COOH)hArrunderset((C ))(CH_(3)CH_(2)COOH)+underset((D))((F_(3)"CC"H_(2)CO)_(2)O)`