Question

Starting with acetylene and 1-bromobutane as the only sources of carbon atoms, show how to synthesize the following. (a) meso-5,6-Decanediol (b) racemic 5,6-Decanediol (c) 5-Decanone (d) 5,6-Epoxydecane (e) 5-Decanol (f) Decane (g) 6-Methyl-5-decanol (h) 6-Methyl-5-decanone

Short answer

Answer: To synthesize 6-methyl-5-decanone from 1-bromobutane and acetylene: Step 1: Convert 1-bromobutane to butylmagnesium bromide (Grignard reagent) by reacting with magnesium in dry ether (Mg, Et2O). Step 2: React butylmagnesium bromide with 2-butanone (CH3COCH2CH3) and then acidify the mixture (with HCl or H2O) to form 6-methyl-5-decanone.

Step-by-step solution

Hydroboration of acetylene

React acetylene with diborane (BH3•THF) followed by oxidation (H2O2, OH-) to form prop-1-ene-1,3-diol.

Conversion to Grignard reagent

Convert 1-bromobutane to a Grignard reagent by reacting with magnesium in dry ether (Mg, Et2O) to form butylmagnesium bromide.

Grignard reaction with the diol

React prop-1-ene-1,3-diol with butylmagnesium bromide (from Step 2) to form meso-5,6-decanediol. (b) racemic 5,6-Decanediol

Synthesis of racemic prop-1-ene-1,3-diol

React acetylene with HgSO4 and H2SO4 in water to form racemic prop-1-ene-1,3-diol.

Conversion to Grignard reagent

Follow the same procedure as in (a) Step 2 to obtain butylmagnesium bromide.

Grignard reaction with the racemic diol

React racemic prop-1-ene-1,3-diol with butylmagnesium bromide (from Step 2) to form racemic 5,6-decanediol. (c) 5-Decanone

Conversion to Grignard reagent

Follow the same procedure as in (a) Step 2 to obtain butylmagnesium bromide.

Reaction with CO2

React butylmagnesium bromide (from Step 1) with carbon dioxide (CO2) and then acidify the mixture (with HCl or H2O) to form pentanoic acid.

Decarboxylation and oxidation

Heat pentanoic acid with copper(II) oxide (CuO) to carry out decarboxylation and oxidation, forming 5-decanone. (d) 5,6-Epoxydecane

Wurtz reaction

Carry out a Wurtz reaction between two moles of 1-bromobutane with sodium in dry ether (2 Na, Et2O) to form hexane.

Oxidation

Oxidize hexane to hexan-5-one using a strong oxidizing agent, like potassium permanganate (KMnO4) or chromium(VI) oxide (CrO3).

Epoxidation

Epoxidize hexan-5-one using peroxyacids, such as meta-chloroperbenzoic acid (mCPBA) to form 5,6-epoxydecane. (e) 5-Decanol

Conversion to Grignard reagent

Follow the same procedure as in (a) Step 2 to obtain butylmagnesium bromide.

Reaction with formaldehyde

React butylmagnesium bromide (from Step 1) with formaldehyde (H2CO) and then acidify the mixture (with HCl or H2O) to form 5-decanol. (f) Decane

Wurtz reaction

Follow the same procedure as in (d) Step 1 to form hexane.

Addition of acetylene

React hexane with acetylene over Lindlar catalyst (Pd on CaCO3 with lead poisoning) to form decane. (g) 6-Methyl-5-decanol

Conversion to Grignard reagent

Follow the same procedure as in (a) Step 2 to obtain butylmagnesium bromide.

Reaction with acetone

React butylmagnesium bromide (from Step 1) with acetone (CH3COCH3) and then acidify the mixture (with HCl or H2O) to form 6-methyl-5-decanol. (h) 6-Methyl-5-decanone

Conversion to Grignard reagent

Follow the same procedure as in (a) Step 2 to obtain butylmagnesium bromide.

Reaction with 2-butanone

React butylmagnesium bromide (from Step 1) with 2-butanone (CH3COCH2CH3) and acidify the mixture (with HCl or H2O) to form 6-methyl-5-decanone.