3-Carboxydec-3-enoic acid. (Heptylidenesuccinic acid.) Potassium t-butoxide.
- Prepare a solution of potassium t-butoxide in t-butyl alcohol using the following procedure.
- Equip a two-necked, round-bottomed 1-litre flask with a reflux condenser and a pressure-equalising dropping funnel.
- Attach to the top of the condenser a nitrogen inlet system with nitrogen escape valve and place the flask in a magnetic stirrer-heating mantle unit.
- Flush the flask with a stream of dry nitrogen, charge the flask with 375 ml of dry t-butanol and add 19.6g (0.5 mol) of potassium.
- Heat the mixture under reflux until the potassium completely dissolves (c. 4 hours).
- To the cooled solution add a mixture of 122g (0.7 mol) of diethyl succinate and 63g (0.5 mol) of heptanal over half an hour; the reaction is exothermic.
- Finally heat the mixture under reflux for 1 hour.
- Rearrange the condenser for distillation and remove the t-butyl alcohol by vacuum distillation using a water pump.
- Acidify the residue with dilute hydrochloric acid and extract with three 200 ml portions of ether.
- Extract the acidic compounds from the ethereal solution by shaking with 50 ml portions of saturated sodium hydrogen carbonate solution until no more carbon dioxide is evolved.
- Acidify the combined aqueous solutions by the careful addition of concentrated hydrochloric acid.
- Extract the 3-ethoxycarbonyldec-3-enoic acid which separates as an oil with ether, dry the ethereal extract over magnesium sulphate and evaporate the ether solution on a rotary evaporator.
- Saponify the crude half ester by heating it under reflux for 1 hour with 400 ml of 10 per cent sodium hydroxide solution.
- Cool the solution, acidify with concentrated hydrochloric acid and filter the precipitated acid with suction.
- Dissolve the crude acid in the minimum volume of ether (about 200 ml are required) and add the solution to an equal volume of light petroleum (b.p. 60-80 °C).
- Filter the precipitate with suction and recrystallise from benzene.
- The yield of 3-carboxydec-3-enoic acid, m.p. 128-130 °C, 37.3 g (31.6%). The infrared spectrum shows absorptions at 3500-2300 cm⁻¹ (O — H stretch of carboxylic acid), 1700 cm⁻¹ (C=O) and 1640 cm⁻¹ (C=C).
3-Carboxy-3,4-dibromodecanoic acid:
- This reaction should be carried out in a fume cupboard.
- Place 5.3g (0.025 mol) of 3-carboxydec-3-enoic acid, 6.0g (0.038 mol) of bromine and 60 ml of carbon tetrachloride in a 100 ml round-bottomed flask equipped with a magnetic stirrer and reflux condenser.
- Irradiate the stirred mixture with a 100- watt lamp for 6 hours; the dibromide forms and precipitates out during this period.
- Filter the product with suction and wash thoroughly with hexane.
- The yield of 3-carboxy-3,4-dibromodecanoic acid is 7.9g (85%). The acid can be recrystallised from toluene, m.p. 142-143 °C. The infrared spectrum shows absorptions at 3400-2400 cm⁻¹ (O — H stretch of CO₂H) and 1730 cm⁻¹ (C=O).
4-Oxodecanoic acid:
- Dissolve 4.0g of 3-carboxy-3,4-dibromodecanoic acid in 60 ml of 2M sodium hydroxide solution and heat the solution at 80-90 °C for 2 hours.
- Cool to room temperature and acidify with dilute sulphuric acid; carbon dioxide is evolved and a white precipitate is formed.
- Filter the precipitated keto acid from the cold solution and recrystallise from light petroleum (b.p. 40-60 °C).
- 4-Oxodecanoic acid, m.p. 68-69 °C, is obtained; the yield is 1.6g (80%). The infrared spectrum shows absorptions at 3400-2400 cm⁻¹ (OH stretch of CO₂H) and 1700 cm⁻¹ (C=0).
- If the dibromo acid is treated with alkali under milder conditions, for example with 1 m sodium hydroxide solution at 20-25 °C for 0.5 hour, the intermediate y-hexylaconic acid (m.p. 123-125 °C) can be isolated after acidification.
- The infrared spectrum shows absorptions at 3110 cm⁻¹ (C — H stretch, alkene), 1715 and 1745 cm⁻¹ (C=O stretch of carboxylic acid and lactone) and 1630 cm (C=C stretch).
Notes to keep in mind:
1. Great care must be taken in the handling of potassium.
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