Column types Widmer

Fractional distillation. Fig. II, 60, 2 illustrates a set-up for fractional distillation wdth a Hempel-type column and cold finger, the latter to give manual control of the reflux ratio. Any other fractionating colunm, e.g., an all-glass Dufton or a Widmer column may, of course, be used. 

The checkers employed a modified Widmer column1 (Fig. 4) that has been used in many organic laboratories, but not officially described. They also used a Vigreux column (50 cm. effective length, 2.7 cm. inside diameter) the first distillation then required ninety minutes, and the yield was 82-83 Per cent. The final temperature of the reaction mixture and observed boiling point will depend upon the type of apparatus used. 

A solution of 2.5 mol of sodium acetylidc in liquid NHj (p. 17-19) is cooled to —40 C and a vigorous stream of acetylene is introduced for 2 min (31/mjn). The alkyl bromide (2.0 mol) is then added dropwise over 1 h while maintaining the temperature as close as possible to -38 C Stirring at this temperature is continued for another 1.5 h (for the type of stirrer see fig 3), then 300 ml of high-boiling petroleum ether (b.p. >170 C) is added. The mixture is cautiously poured onto 2 kg of finely crushed ice in a 5-1 wide-necked round-bottomed (fig. 13) or conical flask. The reaction flask is rinsed with a small amount of ice water which is added to the bulk. After separation of the layers, three extractions with small amounts of petroleum ether are carried out The extracts are washed with dilute hydrochloric acid and subsequently dried over MgS04. Isolation is carried out as described in exps. 1 and 3, and in Chap. 1-2.6. The product is carefully redistilled through a 40-cm Widmer column. 1-Pentyne, b.p. 

Reversed-phase HPLC can separate polyphenolics of extracts on the basis of polarity. HPLC easily produces better resolution among chemically similar compounds in extracts than conventional chromatographic methods. The operating temperature of the column during reversed-phase HPLC analysis should be controlled for data reproducibility. A change in temperature produces only a minor effect, however, on band spacing in reversed-phase HPLC and produces essentially no effect in normal-phase HPLC (Lee and Widmer, 1996). A range of ambient temperatures is widely used, and elevated temperatures are often applied. The retention times of the peaks are dependent upon the type of column and the combination of various solvents used in the method. 

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