Light petroleum, purification

Lassaigne test, 1039, 1040 defects in, 1043 Lead dioxide, 199 Lead tetracetate, 199, 951 Lessing rings, 92 Leuckart reaction, 561, 567 Liebermann nitroso reaction, 649 Light petroleum, purification of, 174 Ligroin, 174 Linseed oil, 445... 

For smaller batches, purification by washing the product through a short column of acidic alumina with light petroleum ether and evaporation of the solvent is satisfactory. 

A solution of hex-l-yne (4.5 mmol) in THF (1ml) was added slowly to lithium bis(phenyldimethylsilyl)cuprate (Chapter 8) (5 mmol, based on CuCN) at 0°C, and the mixture was stirred for 15min at 0°C. Saturated ammonium chloride solution (1 ml) was added, and stirring was continued for 5 min at 0°C. Light petroleum was then added, and the organic layer was washed with ammonium chloride solution, and dried. Concentration and chromatographic purification on silica gel gave the vinylsilane (4.23 mmol, 94%). 

Without digestion the acid will contain appreciable amounts of the ammonium salt. In an alternative method of purification the crude acid is converted to the insoluble sodium salt. The sodium salt can be recrystallized from 95% ethanol to give flaky white crystals, m.p. 339-340°. Digestion of the sodium salt with 1 part of concentrated hydrochloric add and 1 part of water yields the free acid. From 10 g. of crude acid, 7.3 g. of purified acid can be obtained from the sodium salt. The free acid is reported to crystallize well from toluene and light petroleum ether. ... 

Benzoin la (2 mmol) and zeolite A (2 g) were mixed thoroughly in a mortar and the mixture was transfered to a beaker and irradiated for 6 min. The progress of the reaction was monitored by TLC using CH2CI2 as solvent. The mixture was extracted into methylene chloride and then filtered. The solvent was removed under reduced pressure to afford pure benzil 2a (340 mg, 80%). Further purification was carried out by column chromatography (CH2Cl2-light petroleum, 80 20, v/v) and crystallization in EtOH. 

The commercial grade of this solvent is obtainable in greater than 99.5 per cent purity, in which water and peroxides are the major impurities an inhibitor for peroxide formation may have been added by the manufacturers. Peroxide, if present, must be removed by passage through a column of alumina (see 1. Light petroleum for footnote on the disposal of used alumina), or by shaking with iron(n) sulphate solution as described under diethyl ether before drying and further purification is attempted. If the latter method is employed the solvent should then be dried initially over calcium sulphate or solid potassium... 

Unless the reagent has been recently purchased it may contain substantial amounts of toluene-p-sulphonic acid. The most satisfactory procedure for the purification of the chloride involves dissolving it in the minimum amount of chloroform (about 2.5 ml per g) and diluting with 5 volumes of light petroleum (b.p. 40-60 °C), which precipitates impurities. The filtered solution is treated with decolourising charcoal, filtered and concentrated to small volume when colourless crystals of the pure reagent, m.p. 68 °C, are obtained these should be washed with chilled light petroleum (b.p. 40-60 °C). 

Apparatus 22 is cooled with salt solution (-15 °C) to crystallise phosphonitrilechloride trimer the mixture is held for some time to let ciystals grow and precipitate. Then the ciystals are separated in centrifuge 23, and the mother solution is sent back to tank 19. The obtained crystals of phosphonitrilechloride trimer can be given additional purification, i.e. reciys-tallisation from fresh light petroleum or vacuum distillation at 127 °C and a residual pressure of 17 GPa. 

The solvents used should be as little miscible with water as possible, and must be thoroughly purified from traces of grease. Distillation in apparatus free from cork or rubber is desirable for the final purification. Light petroleum, b.p. 60-70°, is probably the best solvent to use if the substance will not dissolve in that, benzene, mixtures of benzene with up to two-fifths of its volume of alcohol, ethyl acetate, and other solvents may be used. High volatility is desirable in order that the solvent shall disappear from the surface very rapidly also the more miscible with water the solvent is, the deeper it penetrates below the surface such penetration has two effects it may carry the substance down into the interior and cause some of it to be precipitated there instead of spread on the surface also the solvent itself may remain near the surface for some time and set up a temporary surface pressure. This is not, however, over a few hundredths of a dyne per cm., with ordinary solvents. 

Tetramethyl 7-oxabicyclo[2.2.1]hepta-2,5-diene-2,3,5,6-tetracarboxylate (20,1.7 g, 5.2 mmol) in benzene (15 mL) was treated with CHjNj in EtjO (100 mL, from 15 g nitrosomethylurea). After 2 d, the solvents were removed. 2.1 g of the bis-pyrazole was left behind and this was used for the next stage without further purification. The crude bis-pyrazole (300 mg, 0.73 mmol) in EtOAc (300 mL) was photolyzed (Hanau Q 81, Pyrex filter) until the UV maximum at 317 nm had disappeared. On concentrating the solution, colorless crystals precipitated and the tetracyclononane 21 was recrystallized from light petroleum ether (bp 90-100°C) yield 240 mg (93%) mp 103-105°C. 

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