SYNTHESIS OF 2-METHYLHEXAN-2-OL (tertiary alcohol from a ketone)

• The apparatus and experimental details are similar to those given in the pre­vious sections. 

• Prepare a Grignard reagent from 24.5 g (1 mol) of magnesium turnings, 137 g (107 ml, 1 mol) of butyl bromide and 450 ml of sodium-dried ether. 

• Add slowly with rapid stirring, and cooling with ice if necessary, a solu­tion of 58 g (73.5 ml, 1 mol) of dry acetone in 75 ml of anhydrous ether. Allow the reaction mixture to stand overnight. 

• Decompose the product by pouring it on to 500 g of crushed ice; dissolve the precipitated magnesium compounds by the addition of 10 per cent hydrochloric acid or of 15 per cent sulphuric acid. 

• Transfer to a separatory funnel, remove the ether layer and extract the aqueous solution with three 50 ml portions of ether. 

• Dry the combined ether­eal solutions over anhydrous potassium carbonate or anhydrous calcium sul­phate, filter, distil off the ether, and fractionally distil the residue. 

• Collect the 2-methylhexan-2-ol at 137-141 °C. 

• The yield is 105 g (90%). 

• Assign the '³C­n.m.r. absorptions which occur at 6 14.1, 23.4, 26.8, 29.3, 44.0 and 70.8. 

Cognate preparations. 2-Methylpentan-2-ol (tertiary alcohol from a ketone)
Use propylmagnesium bromide and acetone. Collect the tertiary alcohol at 121-124 °C.

trans-1-Ethyny1-3,3,5-trimethykyclohexan-l-ol (tertiary alcohol from a ketone)

• Assemble in a fume cupboard a three-necked, 250-ml round-bottomed flask mounted on a magnetic stirrer unit and equipped with a gas inlet tube terminating in a glass frit for the passage of acetone-free acetylene, and a dropping funnel protected with a calcium chloride guard-tube; insert a calcium chloride tube in the third neck. 

• Place in the flask 60 ml of pure tetrahydrofuran and a magnetic follower. 

• Saturate the tetrahydrofuran with acetylene by passing a rapid stream of the gas through the solvent. 

• Then with the continued passage of acetylene, add dropwise from the funnel over 2 hours a previously prepared solution of ethylmagnesium bromide [from 16.4 g (0.15 mol) of ethyl bromide, 3.7 g (0.154 mol) of magnesium in 100 ml of tetrahydrofuran]. 

• Cool the reaction mixture to 0 °C and add with stirring a solution of 7 g (0.05 mol) of 3,3,5- trimethylcyclohexanone in 20 ml of tetrahydrofuran; the slow passage of  acetylene gas should be continued. 

• Stir the mixture for 1 hour and then pour it into a mixture of 80 g of ammonium chloride and 200 g of crushed ice. Separate the organic layer and extract the aqueous layer with three 25 ml por­tions of tetrahydrofuran. 

• Evaporate the tetrahydrofuran from the combined organic layers, dissolve the residue in 100 ml of ether, dry the solution over magnesium sulphate and evaporate the solvent on a rotary evaporator. 

• Distil the residue and collect the alkynol at b.p. 78-79 °C/8 mmHg; this crystallises on standing and has m.p. 26-27 °C. 

• The yield is 5.6 g (70%). The i.r. spectrum clearly shows characteristic group frequencies at v_max 3450 (OH), 3300 H ) and 2110 cm ^-1  

1,1,3- Triphenylprop-2-yn-1-ol (tertiary alcohol from a ketone)

• Prepare a solu­tion of ethylmagnesium bromide in 50 ml of anhydrous ether from 27.3 g (19 ml, 0.25 mol) of ethyl bromide, 6.0 g (0.25 mol) of magnesium. 

• Cool the solution and add dropwise a solution of 25.5 g (27 ml, 0.25 mol) of phenyl-acetylene in 30 ml of anhydrous ether. 

• Boil the reaction mixture gently under reflux for 2 hours and cool to room temperature. 

• Start the stirrer, add slowly a solution of 45.5 g (0.25 mol) of benzophenone in 50 ml of anhydrous ether, and continue to stir at room temperature for 1.5 hours. 

• Finally boil under reflux for 1 hour and cool in an ice bath. 

• Liberate the prod­uct by adding slowly 55 g of ammonium chloride as a saturated aqueous solu­tion, separate the ether layer and extract the aqueous phase with two 20 ml portions of ether. 

• Dry the combined ether solutions over anhydrous sodium sulphate, and remove the ether on a rotary evaporator. 

• Cool the residual oil in ice and triturate with light petroleum (b.p. 60-80 °C) until the triphenyl­propynol crystallises (1), and recrystallise it from a mixture of benzene and light petroleum (b.p. 60-80 °C). 

• The yield is 35 g (49%), m.p. 78-80 °C.

Notes to keep in mind:

1. If the product fails to crystallise, purify it by distillation under reduced pres­sure, b.p. 190 °C/0.05 mmHg.

1-Vinylcyclobutanol (tertiary alcohol from a ketone).⁶³ 

• A dry, three-necked, 250-ml flask under a nitrogen atmosphere is equipped with a mechanical stirrer, dry-ice condenser, and a small additional funnel. 

• The apparatus is charged with magnesium (7.29 g, 0.30 mol) and dry tetrahydrofuran (25 ml). 

• In the addition funnel is placed vinyl bromide (37.5 g, 0.350 mol) in dry tetra­hydrofuran (75 ml) and about 2 ml of this solution is added to the flask with very rapid stirring to initiate the reaction. 

• After initiation, the remaining vinyl bromide is added slowly to maintain steady reflux. 

• Once all the magnesium has been consumed, the mixture is cooled to 35 °C and a solution of cyclo­butanone (14.0 g, 0.2 mol) in dry tetrahydrofuran (30 ml) is added slowly. 

• The dry-ice condenser is replaced by a normal condenser and the solution is refluxed for 90 minutes. 

• After the flask is cooled to 35 °C, saturated ammonium chloride solution (40 ml) is added dropwise with additional cool­ing and vigorous stirring to effect hydrolysis of the magnesium salts. 

• These salts are collected by suction filtration and washed well with anhydrous ether. 

• The combined filtrate is dried over magnesium sulphate and filtered and the solvent removed on the rotary evaporator. 

• Distillation affords 12.89 g (66%) of 1-vinylcyclobutanol, b.p. 67-68 °C/45 mmHg; i.r. (thin film) 3360, 2290, 1246, 1150, and 920 cm ^-1; p.m.r. (CC1₄, TMS) 61.4-2.2 (m, 6H, ^—(CH2)3^—), 4.0 (broad s, 1H, OH) and 4.9-6.3 (ABX pattern, 3H, CH₂=CH—).