SYNTHESIS OF DIBUTYL ETHER

• The success of this preparation depends on the use of the Dean and Stark apparatus which permits the automatic separation of water produced in the reaction. 

• The quantity of water which should be eliminated, assuming a quantitative conversion of the alcohol (0.67 mol) into the ether, is 6.0 g (0.33 mol). 

• Equip a 250-ml two-necked round-bottomed flask with the Dean and Stark apparatus in the central socket; attach a reflux condenser in the upper joint. 

• Fill the graduated side-arm with water and then drain off 6 ml (the quantity to be formed in the reaction). 

• Place 49 g (61ml, 0.67 mol) of butan-1-ol together with 16 g (9 ml) of concentrated sulphuric acid in the flask. 

• Using a screw-capped cone adapter, insert a thermometer in the side socket of the flask with the bulb immersed in the liquid. 

• Heat the flask gently so that the liquid refluxes from the condenser. 

• Water and butan-1-ol will collect in the graduated side-arm and when this is full automatic separation of the two liquids will commence; the water will fall to the bottom of the tube and the lighter butan-1-ol will pass back into the flask. 

• Continue the heating until the temperature in the flask rises to 134-135 °C (after about 30-40 minutes). At this stage 5-6 ml of additional water will have collected in the graduated side-arm and the reaction may be regarded as complete. 

• Further heating will merely result in considerable darkening of the mixture in the flask and the forming of the highly flammable but-1-ene. 

• Allow the reaction mixture to cool or cool the flask under running water from the tap. 

• Pour the contents of the flask and water-separator tube into a separatory funnel containing 100 ml of water, shake well and remove the upper layer containing the crude ether mixed with a little unchanged butanol. 

• Shake the crude ether with 25 ml of cold 50 per cent by weight sulphuric acid (from 20 ml of concentrated acid cautiously poured into 35 ml of water) (1) for 2-3 minutes, separate the upper layer and repeat the extraction with another 25 ml of the acid. 

• Finally wash twice with 25 ml portions of water; dry with 2 g of anhydrous calcium chloride (2). Filter through a fluted filter paper into a 50 ml flask and distil. 

• Collect the dibutyl ether at 139-142 °C. The yield is 15 g (34%). Record the i.r. spectrum and compare it with Fig. 3.24. Interpret the m.s. of dibutyl ether which shows principal fragmentation ions at m/z 87, 57 (base peak), 56, 41, 29 and 27.

Notes to keep in mind: 

1. This separation utilises the fact that butan-1-ol is soluble in 50 per cent sulphuric acid by weight, whereas dibutyl ether is only slightly soluble.

2. An alternative method for isolating dibutyl ether utilises the fact that butan-1-ol is soluble in saturated calcium chloride solution while dibutyl ether is slightly soluble. Cool the reaction mixture in ice and transfer to a separatory funnel. Wash cautiously with 100 ml of 2.5-3 m sodium hydroxide solution; the washings should be alkaline to litmus. Then wash with 30 ml of water, followed by 30 ml of saturated calcium chloride solution. Dry with 2-3 g anhydrous calcium chloride.

Cognate preparation: Dihexyl ether

• Use 68 g (83 ml, 0.67 mol) of hexan-1-ol (b.p. 156-157 °C); heat until the temperature rises to 180 °C. 

• Pour the reaction mixture into water, separate the upper layer, wash it twice with 5 per cent sodium hydroxide solution, then with water, and dry over anhydrous potassium carbonate. 

• Distil and collect the fractions of b.p. (i) 160-221 °C (23 g) and (ii) 221-223 °C (23 g). 

• Reflux fraction (i) with 5g of sodium and distil from the excess of sodium when a further quantity of fairly pure dihexyl ether (1 3 g, fraction (iii)) is thus obtained. 

• Combine fractions (ii) and (iii) and distil from a little sodium; collect the pure dihexyl ether (26 g, 42%) at 221.5—223 °C.