Q17-47E - Organic Chemistry (Mcmurry)

Question

Question: How would you prepare the following compounds from

2-phenylethanol?

More than one step may be required.

(a) Styrene$\left(\mathbf{PhCH}\mathbf{=}{\mathbf{CH}}_{\mathbf{2}}\right)$ 

(b) Phenylacetaldehyde$\left({\mathbf{PhCH}}_{\mathbf{2}}\mathbf{CHO}\right)$ 

(c) Phenylacetic acid$\left({\mathbf{PhCH}}_{\mathbf{2}}{\mathbf{CO}}_{\mathbf{2}}\mathbf{H}\right)$

(d) Benzoic acid

(e) Ethylbenzene

(f) Benzaldehyde

(g) 1-Phenylethanol

(h) 1-Bromo-2-phenylethane

Step-by-Step Solution

Answer

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Step 1: Reactions of alcohols

Alcohols get converted to alkenes when reacted with ${\mathbf{POCl}}_{\mathbf{3}}$ and pyridine. Primary alcohols are oxidized to aldehydes and secondary alcohols are oxidized to ketones in the presence of Dess-Martin periodinate. Alcohols produce alkyl bromides when treated with ${\mathbf{PBr}}_{\mathbf{3}}$

Step 2: Proposing structure of several compounds from the NMR spectrum

(a) The compound 2-Phenyl-ethanol reacts with ${\mathrm{POCl}}_3$ and pyridine to form styrene. The reaction can be given as:

                                                         Reaction (a)

(b) The compound 2-Phenyl-ethanol reacts with periodinane and ${\mathrm{CH}}_2{\mathrm{Cl}}_2$to form phenylacetaldehyde. The reaction can be given as:

                                                           Reaction (b)

(c) The compound, 2-Phenylethanol reacts with ${\mathrm{CrO}}_3$
 and ${\mathrm{H}}_3{\mathrm{O}}^{+}$ to form phenylacetic acid. The reaction can be given as:

                                                           Reaction (c)

(d) The compound, 2-Phenylethanol reacts with ${\mathrm{KMnO}}_4$and${\mathrm{H}}_2\mathrm{O}$ to form benzoic acid. The reaction can be given as:

                                                           Reaction (d)

(e) The compound 2-Phenyl-ethanol reacts with ${\mathrm{POCl}}_3$ and pyridine to form styrene. This further reacts with ${\mathrm{H}}_2$ and Pd to form ethylbenzene. The reaction can be given as:

                                                           Reaction (e)

(f) The compound 2-Phenyl-ethanol reacts ${\mathrm{POCl}}_3$ with and pyridine to form styrene. This further reacts with ${\mathrm{O}}_3$ , zinc and ${\mathrm{H}}_3{\mathrm{O}}^{+}$ to form benzaldehyde. The reaction can be given as:

                                                           Reaction (f)

(g) The compound 2-Phenyl-ethanol reacts with ${\mathrm{POCl}}_3$ and pyridine to form styrene. This further reacts with $\mathrm{Hg}{\left(\mathrm{OAc}\right)}_2$, water and sodium borohydride to form 1-Phenylethanol.The reaction can be given as:

                                                           Reaction (g)

(h) The compound 2-Phenyl-ethanol reacts with ${\mathrm{PBr}}_3$ to form 1-Bromo-2-Phenylethane. The reaction can be given as:

                                                           Reaction (h)