1-Methoxy-4-(methoxymethyl)benzene, $4 - CH X_{3} O - C X_{6} H X_{4} - CH X_{2} - OCH X_{3}$ , is heated with excess concentrated $HI$ . Assume that every C(sp $^{3}$ )-O bond ends up as a C-I bond (the benzylic ether is cleaved at the benzylic carbon and any alcohol formed is also converted to iodide by $HI$ ), that the aryl C(sp $^{2}$ )-O bond is never cleaved and that the phenol formed does not react further. How many moles of $HI$ are consumed per mole of the ether? Give the answer as an integer.

Numerical answer type, tolerance 0.5.

Answer: 3

Each cleavage of a C(sp

^{3}

)-O bond consumes one

HI

. The benzylic C-O bond is cleaved first:

ArCH X_{2} - OCH X_{3} + HI ArCH X_{2} I + CH X_{3} OH

(1 HI). The methanol formed then reacts:

CH X_{3} OH + HI CH X_{3} I + H X_{2} O

(1 HI). The aryl methyl ether gives

ArOH + CH X_{3} I

(1 HI) and the aryl C-O bond stays intact. The total is 3 mol of HI per mole of ether.