SYNTHESIS OF HEXACOSANE

STEP 1: Dissolve 5.0 g of pure myristic acid (tetradecanoic acid) in 25 ml of absolute methanol to which 0.1 g of sodium has been added. 

STEP 2: Place the solution in a cylindrical cell (25 cm long, 3 cm diameter) provided with two platinum plate electrodes (2.5 x 2.5 cm) set 1-2 mm apart. 

STEP 3: Electro­lyse at about 1 amp until the electrolyte is just alkaline (pH 7.5-8). 

STEP 4: Cool the cell in an ice bath during the electrolysis. 

STEP 5: Reverse the current from time to time; this will help to dislodge the coating of insoluble by-products on the electrodes. 

STEP 6: Neutralise the cell contents by adding a few drops of glacial acetic acid, and evaporate most of the solvent under reduced pressure using a rotary evaporator. 

STEP 7: Pour the residue into the water and extract the crude product with ether. 

STEP 8: Wash the ethereal solution with dilute sodium hydroxide solution, dry (magnesium sulphate) and evaporate the solvent. 

STEP 9: Recrystallise the resi­due from light petroleum (b.p. 40-60 °C). 

STEP 10:The yield of hexacosane, m.p. 57­58 °C is 2.4 g (65%).

SYNTHESIS OF UNDECANE

STEP 1: Place 9.53 g (0.05 mol) of copper(i) iodide in a two-necked, 500-m1 round-bottomed flask containing a glass-covered magnetic follower bar. 

STEP 2: Fit a rubber septum to one of the necks of the flask and connect the other neck to one arm of a three-way stopcock. 

STEP 3: Connect the second arm of the stopcock to a supply of dry, oxygen-free nitrogen and the remaining arm to a vacuum pump. 

STEP 4: Evacuate the flask by opening the stopcock to the vacuum pump (1) and then, with a rapid stream of nitrogen flowing, carefully open the stopcock to the nitrogen supply to fill the flask with nitrogen. Repeat this process twice; flame the flask gently on the final occasion it is evacuated. Maintain a static atmosphere of nitrogen in the flask throughout the reaction by passing a slow stream of nitrogen through the nitrogen line. Cool the flask in an acetone/Cardice bath and transfer 100 ml of dry tetrahydrofuran (2) to the flask via the septum using a hypodermic syringe (3). 

STEP 5: Stir the cooled (— 78 °C) suspension and add 52.0 ml of a 1.92 molar solution of butyllithium in hexane (4) from a hypodermic syringe. 

STEP 6: Stir the flask solution at — 78 °C for 1 hour, and then add a solution of 3.39 g (0.015 mol) of 1-iodoheptane in 10 ml of dry tetrahydrofuran dropwise from the syringe. 

STEP 7: Stir the solu­tion at —78 °C for 1 hour and then at 0 °C (ice bath) for a further 2 hours ((5) and (6)). 

STEP 8: Hydrolyse the reaction mixture by pouring it carefully into 100 ml of 1 M hydrochloric acid. 

STEP 9: Separate the upper organic layer and extract the aqueous layer with two 50 ml portions of pentane. 

STEP 10: Wash the combined organic layers with water (50 ml), dry over magnesium sulphate and evapor­ate the solvents on the rotary evaporator. 

STEP 11: Distil the residue at atmospheric pressure using a semimicro scale distillation unit fitted with a short fractio­nating side-arm packed with glass helices. 

STEP 12: Undecane has b.p. 194-197 °C; the yield is 1.24 g (53%).

Notes to keep in mind:

1. This operation should be carried out behind a safety screen.

2. Tetrahydrofuran should be freshly distilled from lithium aluminium hydride. It is convenient to store a supply of peroxide-free tetrahydrofuran under nitrogen over lithium aluminium hydride and distil appropriate quantities as required.

3. The syringes and long flexible needles can be obtained from Aldrich Chemical Co.

4. Solutions of butyllithium, and other lithium reagents, may be purchased from Aldrich.

5. The progress of the reaction may be conveniently followed by g.l.c. Remove samples (c. 2-3 ml) from the reaction mixture by means of a hypodermic syringe and submit them to a small-scale hydrolysis and extraction procedure similar to that described for the main reaction mixture. Analyse the organic layer on a 10 per cent squalane on Chromosorb W column held at 140 °C. Under these conditions 1-iodo­heptane has a slightly longer retention time than undecane.

6. Complete reaction of the alkyllithium can be tested by means of the Gilman test.

SYNTHESIS OF 7-ACETOXYHEPTANAL

STEP 1:           1-Acetoxy-4-iodobutane

• A 500-ml flask is fitted with an addition funnel, condenser and magnetic stirrer. Tetrahydrofuran (50 ml, 0.61 mol), acetic anhydride (100 ml, 1.0 mol), zinc dust (0.1 g, 1.5 mmol) are placed in it. Aqueous hydriodic acid (55%, 40 ml, 0.29 mol) is added dropwise at a rate that keeps the exothermic reaction at reflux.
• After the addition is complete, the mixture is allowed to cool for 1 hour and then poured into 200 ml of saturated aqueous sodium carbonate.
• The mixture is extracted with dichloromethane, dried with magnesium sulphate and the solvent evaporated.
• The residual oil is distilled to give the product, yield 56.7 g (80%), b.p. 76-78 °C/0.5 mmHg; p.m.r. (CDC1₃, TMS) 6 1.88 (m, 4H), 2.02 (s, 3H), 3.20 (t, 2H, J = 6 Hz, —CH₂I) 4.05 (t, 2H, J = 6 Hz, —CH₂.0Ac).

STEP 2:           2-(6-Acetoxyhexyl)-1,3-dioxane

• Copper(i) iodide (0.60 g, 3.1 mmol) and 1- acetoxy-4-iodobutane (12.1 g, 50.0 mmol) are cooled in a dry ice/propan-2-ol bath under a nitrogen atmosphere (1). 
• The Grignard reagent (2), prepared from 2-(2-bromoethyl)-1,3-dioxane' (12.19 g, 62.5 mmol) in 50 ml of tetra­hydrofuran, is added dropwise to the cooled solution. 
• This is stirred at —80 °C for 30 minutes, slowly raised to reflux temperature over a 2-hour period, and then heated at reflux for 6 hours. 
• The tetrahydrofuran is removed by rotary evaporation and the residue poured into aqueous ammonia/ ammonium chloride solution (800 ml). 
• The product is extracted with ether (3 x 50 ml), dried with magnesium sulphate and distilled.
•  A small amount of 1-acetoxy-4-iodobutane is recovered, and then the product is obtained in a yield of 8.86 g (77%), b.p. 90-100 °C/0.3 mmHg.

STEP 3:           7-Acetoxyheptanal 

• 2-(6-Acetoxyhexyl)-1,3-dioxane (4.60 g, 20.0 mmol), methanol (150 ml), glacial acetic acid (35 ml) and concentrated hydrochloric acid (1 ml) are stirred and left to stand for 3 days. 
• This mixture is poured cautiously into saturated sodium hydrogen carbonate solution (500 ml) and the product extracted with ether (3 x 200 ml). 
• The extract is dried with mag­nesium sulphate and evaporated to give the crude dimethyl acetal, which is then dissolved in glacial acetic acid (100 ml), water (10 ml) and hydrochloric acid (1 ml) and left to stand for 3 days. 
• The solution is poured cautiously into saturated aqueous sodium hydrogen carbonate (1 litre), made basic with additional sodium hydrogen carbonate, and the product extracted with ether (3 x 50 ml). 
• The extract is dried with magnesium sulphate, evaporated and the residue distilled to give the product, yield 3.10 g (90%), b.p. 93-98 °C/ 0.7 mmHg.

Notes to keep in mind:

1. The editors suggest that the apparatus consists of a 100-m1 two-necked flask fitted with a silicone rubber septum into which is inserted a syringe needle connected to a nitrogen feed and through which the reagents may be syringe-injected; the second arm of the flask is fitted with a reflux condenser the outlet of which is connected to a mercury bubbler.

2. The Grignard reagent is prepared by the following procedure ^{1 6}' with suitable adjustment of the quantities of reagents employed. A 50-m1 flask is equipped with a reflux condenser, a nitrogen atmosphere and magnetic stirring. In it are placed magne­sium turnings (0.97 g, 40 mmol), dry tetrahydrofuran (25 ml) and 2-(2-bromoethyl)- 1,3-dioxane^{l 6b}(5.85, 30 mmol) (or from Aldrich). This is heated to reflux and the heat immediately removed.The exothermic reaction is moderated at reflux by the occa­sional application of an ice bath. After 10 minutes, heat is applied to maintain reflux­ing for an additional 10 minutes. After cooling to room temperature the solution is drawn up into a 50-m1 syringe leaving excess magnesium behind. 

SYNTHESIS OF HEPT-1-ENE

STEP 1: In a 1-litre three-necked flask prepare the Grignard reagent, butylmagnesium bromide, from 12.2 g (0.5 mol) of dry magnesium turnings, a small crystal of iodine, 68.5 g (53 ml, 0.5 mol) of butyl bromide and 260 ml of anhydrous ether. 

STEP 2: Equip a 500-m1 three-necked flask with a sealed stirrer unit, a 100-m1 separatory funnel and a double surface condenser. Force the solution of the Grignard reagent with the aid of pure, dry nitrogen and a tube containing a plug of purified glass wool (1) into the 500-m1 flask through the top of the double surface con­denser. 

STEP 3: Charge the separatory funnel with a solution of 50 g (35 ml, 0.42 mol) of allyl bromide in 25 ml of anhydrous ether; place calcium chlor­ide drying tubes into the top of the double surface condenser and of the drop­ping funnel. Immerse the flask containing the Grignard reagent in cold water,stir vigorously, and add dip allyl bromide at such a rate that the ether boils gently; cool momentarily in ice if the reaction becomes too vigorous. 

STEP 4: It is im­portant that the allyl bromide reacts when added, as indicated by gentle boil­ing of the solution (2). 

STEP 5: When all the allyl bromide has been introduced, continue stirring for 45 minutes while refluxing gently by immersing the flask in a bath of warm water. 

STEP 6: Allow to cool (3). 

STEP 7: Pour the reaction mixture cautiously on to excess of crushed ice contained in a large beaker. 

STEP 8: Break up the solid magnesium complex and decompose it with ice and dilute sulphuric acid or concentrated ammonium sulphate solution. 

STEP 9: Separate the ether layer, wash it with ammoniacal ammonium sulphate solution to remove any dis­solved magnesium salts and dry over magnesium sulphate. 

STEP 10: Distil the dry ethereal solution through a fractionating column: after the ether has passed over, collect the hept-l-ene at 93-95 °C. The yield is 29 g (71%).

   Notes to keep in mind:

    1. Solid magnesium must be absent to avoid the formation of biallyl via allyl 

magnesium bromide; the insertion of a short plug of glass wool effectively removes
any finely divided magnesium or alternatively use a tube terminating in a glass frit.

    2. If reaction does not occur when a little allyl bromide is first introduced, further addition must be discontinued until the reaction has commenced. Remove 2-3 ml of the Grignard solution with a dropper pipette, add about 0.5 ml of allyl bromide and warm gently to start the reaction; after this has reacted well, add the solution to the main portion of the Grignard reagent.

   3. A slight excess of Grignard reagent should be present at this stage. Test for the presence of the reagent as follows. Remove 0.5 ml of the clear liquid with a dropper pipette and add 0.5 ml of a 1 per cent solution of Michler's ketone [4,4'-bis(dimethyl­amino)benzophenone] in benzene, followed by 1 ml of water and 3-4 drops of 0.01 M iodine in glacial acetic acid; shake. A greenish-blue colour results if a Grignard reagent is present. In the absence of iodine, the colour fades. A dye of the diphenylmethane type is produced.

SYNTHESIS OF OCTANE

STEP 1: Weigh out 23 g (1 mol) of clean sodium under sodium-dried ether, cut it up rapidly into small pieces and introduce the sodium quickly into a dry 750- or 1000-m1 round-bottomed flask. 

STEP 2: Fit a dry 30-cm double surface condenser (e.g. of the Davies type) into the flask and clamp the apparatus so that the flask can be heated on a wire gauze. 

STEP 3: Weigh out 68.5 g (53 ml, 0.5 mol) of butyl bromide previously dried over anhydrous sodium sulphate. 

STEP 4: Introduce about 5 ml of the bromide through the condenser into the flask. 

STEP 5: If no reaction sets in, warm the flask gently with a small lumin­ous flame; remove the flame immediately reaction commences (the sodium will acquire a blue colour). 

STEP 6: When the reaction subsides, shake the contents of the flask well; this will generally produce further reaction and some of the sodium may melt. 

STEP 7: Add a further 5 ml of butyl bromide, and shake the flask. 

STEP 8: When the reaction has slowed down, repeat the above process until all the alkyl bromide has been transferred to the flask (about 1.5 hours). 

STEP 9: Allow the mixture to stand for 1-2 hours. 

STEP 10: Then add down the condenser by means of a dropping funnel 50 ml of rectified spirit dropwise over 1.5 hours, followed by 50 ml of 50 per cent aqueous ethanol during 30 minutes, and 50 ml of distilled water over 15 minutes; shake the flask from time to time. 

STEP 11: Add 2-3 small pieces of porous porcelain and reflux the mixture for 3 hours; any unchanged butyl bromide will be hydrolysed. 

STEP 12: Add a large excess (500-750 ml) of water, and separate the upper layer of crude octane (17-18 g). 

STEP 13: Wash it once with an equal volume of water, and dry it with magnesium sulphate. Distil through a short fractioning side-arm and collect the fraction, b.p. 123­126 °C (15 g, 52%) (1).

Notes to keep in mind:

1. All hydrocarbons prepared by the Wurtz reaction contain small quantities of unsaturated hydrocarbons. These may be removed by shaking repeatedly with 10 per cent of the volume of concentrated sulphuric acid until the acid is no longer coloured (or is at most extremely pale yellow); each shaking should be of about 5 minutes' duration. The hydrocarbon is washed with water, 10 per cent sodium car­bonate solution, water (twice), and dried with magnesium sulphate or anhydrous cal­cium sulphate. It is then distilled from sodium; two distillations are usually necessary.

SYNTHESIS OF UNDECANE

STEP 1: To a slurry of undecan-6-one toluene-p-sulphonylhydrazone (5.08 g, 15 mmol) (1) in 50m1 of glacial acetic acid is added sodium borohydride pellets (c. 5.67 g, 150 mmol, 24 pellets) (2) at such a rate that foaming is not a problem (c. 1 hour).

STEP 2: The solution is stirred at room temperature for 1 hour and then at 70 °C for 1.5 hours. 

STEP 3: The solution is then poured into crushed ice, made basic with aqueous sodium hydroxide and extracted with three por­tions of pentane. 

STEP 4: The pentane solution is dried and concentrated in a rotary evaporator, and the residue distilled at reduced pressure (Kugelrohr appar­atus) to obtain 1.96 g (84%) of undecane. 

STEP 5: Undecane has b.p. 87 °C/20 mmHg.

Notes to keep in mind:

1. The hydrazones are prepared by the following general procedure.' The carbonyl compound and a 10 per cent molar excess of toluene-p-sulphonylhydrazine in absolute ethanol (c. 2 ml per gram of carbonyl compound) are heated on a steam bath until a clear solution results (15 minutes). Cooling affords crystalline products in good to excellent yields. Recrystallisation is accomplished from ethanol or aqueous acetone. For hindered ketones periods of up to 14 hours of reflux are suggested.

2. Obtainable from Alfa Inorganics.

SYNTHESIS OF HEPTANE

STEP 1: Place 100 g (1.53 mol) of zinc wool in a 1-litre three-necked flask and amal­gamate it. 

STEP 2: Fit the flask with a sealed stirrer unit, an efficient double surface condenser and a lead-in tube dipping almost to the bottom of the flask for the introduction of hydro­gen chloride gas; insert an empty wash bottle between the hydrogen chloride generator and the flask. 

STEP 3: Introduce through the condenser 250 ml of concentrated hydrochloric acid and 50 ml of water, set the stirrer in motion and then add 40 g (0.35 mol) of heptan-4-one. 

STEP 4: Pass a slow current of hydrogen chloride through the mixture; if the reaction becomes too vigorous, the passage of hydrogen chloride is tempor­arily stopped. 

STEP 5: After 2-3 hours most of the amalgamated zinc will have reacted. 

STEP 6: Leave the reaction mixture overnight, but disconnect the hydrogen chloride gas supply first. 

STEP 7: Remove the stirrer and the condenser from the flask. Arrange for direct steam distillation from the flask by fitting a stopper into one neck, a knee tube connected to a downward condenser in the central aperture and connect the lead-in tube to a source of steam. 

STEP 8: Stop the steam distillation when the distillate passes over as a clear liquid. Separate the upper layer, wash it twice with distilled water, dry with magnesium sulphate or anhydrous calcium sulphate and distil through a short fractionating column. 

STEP 9: Collect the fraction, b.p. 97-99 °C (1). The yield of heptane is 26 g (74%).

Notes to keep in mind:

1. The products of most Clemmensen reductions contain small amounts of unsaturated hydrocarbons. These can be removed by repeated shaking with 10 per cent of the volume of concentrated sulphuric acid until the acid is colourless or nearly so; each shaking should be of about 5 minutes duration. The hydrocarbon is washed with water, 10 per cent sodium carbonate solution, water (twice), dried with magne­sium sulphate or anhydrous calcium sulphate and finally fractionally distilled over sodium.

SYNTHESIS OF CYCLOOCTANE

STEP 1: An oven-dried 300-m1 flask, equipped with a side-arm fitted with a silicone rubber septum, a magnetic stirrer bar, and a reflux condenser connected to a mercury bubbler, is cooled to room temperature under a stream of dry nitro­gen. 

STEP 2: Tetrahydrofuran (20 ml) is introduced, followed by 7.1 g (25 mmol) of cyclooctyl tosylate (1).

STEP 3: The mixture is cooled to 0 °C (ice bath).

STEP 4: To this stirred solution, lithium triethylborohydride [33.3 ml (50 mmol) of a 1.5 M solution in tetrahydrofuran] is added, and the ice bath removed. 

STEP 5: The mixture is stirred for 2 hours (c. 25 °C). Excess hydride is decomposed with water. 

STEP 6: The organoborane is oxidised with 20 ml of 3 m sodium hydroxide solution and 20 ml of 30 per cent hydrogen peroxide [(2) and (3)]. Then the tetrahydrofuran layer is separated. 

STEP 7: The aqueous layer is extracted with 2 x 20 ml portions of pentane. 

STEP 8: The combined organic extracts are washed with 4 x 15 ml portions of water to remove ethanol produced in the oxidation. The organic extract is dried (MgSO₄) and volatile solvents removed by distillation (2). 

STEP 9: Distillation of the residue yields 2.27 g (81%) of cyclooctane as a colourless liquid, b.p. 142-146 °C, nU1.4630.

Notes to keep in mind:

1. The editors emphasise the CAUTIONARY notes relating to the handling of hydrogen peroxide, and to the distillation of extracts following the use of tetrahydrofuran/hydrogen peroxide in oxidation procedures.

SYNTHESIS OF HEXANE

STEP 1: In a suitably equipped 500 ml three-necked flask prepare an ether solution (100 ml) of hexylmagnesium bromide from 12 g (0.5 mol) of magnesium turn­ings and 82.5 g (70.5 ml, 0.5 mol) of dry 1-bromohexane. 

STEP 2: When most of the magnesium has dis­appeared (about 4 hours) add AnalaR ammonium chloride (27 g) and leave the reaction mixture overnight. 

STEP 3: Cool the flask in ice and add slowly a large excess of dilute hydrochloric acid; the precipitate will dissolve completely. 

STEP 4: Separate the upper ethereal layer, and wash it successively with dilute hydro­chloric acid and water; dry with magnesium sulphate or anhydrous calcium sulphate.

STEP 5:  Distil the ethereal solution through an efficient fractionating col­umn (e.g. a Hempel column filled with 6-mm glass or porcelain rings, or a 30-cm all-glass Dufton column). 

STEP 6: After the ether has passed over, hexane will distil at 67-70 °C (13-14 g, 30-33%). Record the i.r. spectrum and compare it with Fig. 3.13(a). The m.s. shows principal frag­ment ions at m/z 86 (M), 57 (M — C₂H₅, base peak), 43 (M — C₃H₇) and 29 (C2H5^6°)•

SYNTHESIS OF 5,6-DIHYDRO-ENDO-DICYCLOPENTADIENE

Dicyclopentadiene is chilled until a major proportion has solidified. The material is filtered and the solid is pressed on a Buchner funnel with a spatula to remove as much liquid as possible. The solid is warmed just to melt and the process is repeated. The resulting solid has m.p. 28-30 °C m.p. 27-28 °C).

STEP 1: In a 2-litre flask, 37.5 g (150 mmol) of nickel(n) acetate tetrahydrate (1) are dissolved in 200 ml of 95 per cent ethanol. The flask is attached to a Brown^e hydrogenator and flushed with hydrogen.

STEP 2: With rapid stirring 150 ml of 1.0 M sodium borohydride solution in ethanol (2) is added to reduce the nickel acetate to P-2 nickel.

STEP 3: The purified endo-dicyclopentadiene (407 g, 3.08 mol) is melted with 200 ml of ethanol and the mixture injected into the hydrogenator.

STEP 4: With vigorous stirring, the reaction proceeds smoothly; hydrogen uptake ceases when 3.08 mol of hydrogen has been absorbed.

STEP 5: Five grams of activated carbon are added to the reaction mixture to aid in catalyst removal, and the warm (40 °C) mixture is filtered through a thin (c. 3 mm) pad of carbon on a Buchner funnel.

STEP 6: The filter pad is washed with 2 x 100 ml of warm acetone.

STEP 7: The combined organic layers are distilled to remove solvent.

STEP 8: The residue is distilled through a short Vigreux column to give 370 g, 2.76 mol (90%) of 5,6-dihydro-endo-dicyclopentadiene, b.p. 178­180 °C, m.p. 48-50 °C.

STEP 9: Recrystallisation from methanol gives m.p. 50 °C (lit.' 48.5-50 °C); p.m.r. (CC1₄, TMS), 6 1.25 (s, 3.8H), 1.45 (s, 2.2H), 2.0-3.2 (m, broad, 6.2H), 5.70 (s, broad, 2.0H). The product was free from starting material by g.l.c. analysis.

Notes to keep in mind:

1. The nickel(n) acetate tetrahydrate was AnalaR grade.

2. A stabilised solution suitable for catalytic reduction was prepared by dissolving 4.0 g of sodium borohydride powder in a mixture of 95 ml of absolute ethanol and 5 ml of 2 M sodium hydroxide and filtering the resulting solution. This solution is best pre­pared freshly the day of use for maximum catalyst reproducibility but may be utilised satisfactorily for up to 5 days if kept refrigerated. Formation of small amounts of sedi­ment under refrigeration is not harmful.

3. Details of a procedure for smaller scale exploratory experiments are given as follows.' Nickel(u) acetate tetrahydrate (1.24 g, 5.00 mmol) is dissolved in (50 — n) ml (n — volume of substrate to be added) of 95 per cent ethanol in a 125 ml Erlenmeyer flask (modified for high stirring). The flask is attached to a borohydride hydrogenator, which is then flushed with nitrogen. With vigorous stirring, 5.0 ml of 1.0 M sodium borohydride solution in ethanol (see above) is injected over 15 seconds. When gas evolution from the mixture ceases, the catalyst is ready for use. The hydrogenator is purged with hydrogen and the reaction initiated by injecting the substrate. Addition of solid substrates is accomplished with the stirrer stopped, just before purging with hydrogen. Samples for analysis are withdrawn from the reactor with a syringe and stainless steel needle. Gas chromatographic columns which are found to be useful have stationary phases of either adiponitrile, triethylene glycol—silver nitrate, tris­(cyanoethoxy)propane, UCON 50 HB 2000, and squalene.

SYNTHESIS OF 2-METHYLBUTANE

STEP 1: Place 100 mg of Adams' platinum dioxide catalyst and 9.8 g (0.14 mol) of 2-methylbut-2-ene in a 100-m1 hydrogenation flask.

STEP 2: Attach the flask to the adapter of the atmospheric hydrogenation apparatus and cool the lower part in an ice-water bath.

STEP 3:  Fill the flask and gas burettes with hydrogen by the hydrogenation procedure; note the volumes in the gas burettes, remove the cooling bath and gently agitate the flask.

STEP 4: When uptake of hydro­gen ceases (the catalyst often coagulates and collects at the bottom of the flask at this stage), note the total volume of hydrogen absorbed; this should be in the region of 3 litres.

STEP 5: Cool the flask contents and follow the procedure for replacing the hydrogen in the apparatus with air.

STEP 6: Disconnect the hydro­genation flask and with a suitably sized dropper pipette transfer the liquid to a small distillation flask leaving the catalyst in the hydrogenation flask (1).

STEP 7: Distil the 2-methylbutane (b.p. 30 °C) using a small ice-cooled water con­denser with the receiver flask immersed in an ice-salt cooling bath (2).

STEP 8: The yield is 7 g (70%). Record the i.r. spectrum and compare it with the spectrum of the starting material (3).

STEP 9: Note (a) the disappearance upon hydrogenation of the absorption bands at 810 and 1675 cm ^-1 (due to the out-of-plane deformation of the =C—H bond and the stretching of the carbon-carbon double bond respectively) in the alkene, and (b) the replacement of the peak at 1380 cm ^-1 in the alkene (—CH₃ bending mode) by a doublet at 1385 and 1375 cm ^-1 ((CH₃)₂C— plus terminal —CH₃).

STEP 10: The m.s. shows principal frag­ment ions at m/z 72 (M), 57 (M—CH₃), 43 (M—C₂11₅, base peak) and at 29(C2 H5 ^GI).

Notes to keep in mind:

1. This technique, rather than conventional filtration, is to be preferred in this case owing to the high volatility of the hydrocarbon. For more details you can refer disposal and recovery of the catalyst, Hydrogenation at atmospheric pres­sure(12).

2.  An alternative and convenient arrangement is to supply the condenser with cooled water from an ice/water reservoir by means of a peristatic pump.

3. In both cases a fixed path length cell (0.025 mm) should be employed.