Separation Of Propyl Acetate

The third fractionation, III, was carried out in a similar manner, a new fraction, No. 3, being collected at the beginning. As the temperature rose to 101.55°, the boiling point of propyl acetate, before the end of the last distillation, the residue was placed in a separate flask, z, and was not redistilled. The residues from subsequent fractionations up to the 10th were collected in z, but after this, as a large amount of propyl acetate had been removed, the temperature did not reach 101.55° and the residue from the 11th fractionation (b.p. above 101.45°) was placed in a new flask, y. At the end of the 12th fractionation the temperature rose only to 101.15° and the residue was placed in a third flask, x, and subsequently the residues were placed in w, v . . . . q, as shown in Table 40.

Separation Of Methyl Acetate

It was not until the 5th fractionation that the first fraction began to boil at 57.1°, the boiling point of methyl acetate, and it was not thought advisable to separate the first portion of the first distillate until the 8th fractionation. This portion and also the corresponding ones up to the 20th fractionation were collected together in a flask, a, after which the first portions were collected in b, c, d and e.

Accumulation Of Ethyl Acetate In Middle Fractions

The presence of the middle substance, ethyl acetate, is not clearly indicated until the 4th fractionation, when the value of Aw/At for the 6th distillate (No. 11) is somewhat higher than for those above and below it; but the gradual accumulation of the ethyl acetate in the middle fractions in subsequent fractionations is clearly shown by the rise in the value of Aw I At for the fractions 8 and 11 and, after the 10th fractionation, for fractions 9 and 10. The range of temperature for Nos. 9 and 10 was gradually diminished from 0.2° each in the 11th fractionation until no rise could be detected ; there was, indeed, no perceptible rise of temperature during the collection of No. 11 in the 22nd and 23rd fractionations. It was therefore certain that after the 26th fractionation the tenth fraction was free from propyl acetate, and that the remaining fractions b to e and 5 to 10 contained only methyl and ethyl acetates. Similarly, it is safe to conclude that the fractions Q to z were free from methyl acetate. The preliminary series of fractionations was therefore completed, no fraction now containing more than two components.

Graphical Representation Of Results

The progress of the separation is well seen by mapping the temperatures against the percentage weights of distillate collected, and the curves for the first twelve fractionations are shown in Fig. 35 (a and b). The horizontal lines at the extremities of the later curves represent the methyl and propyl acetates removed in the first portion of the first distillates and in the residues respectively. The presence of ethyl acetate is clearly indicated in the fourth curve but not in the earlier ones.

G.35 (a). - Results of fractional distillation of mixture of methyl, ethyl and propyl acetates.

Fig. 35 (b). - Results of fractional distillation of mixture of methyl, ethyl and propyl acetates (continued).

Final Fractionations

The fractions into which the esters had been separated at the end of the 26th fractionation are shown in Table 41. The total weight was 490.8 grams, and therefore 86 grams had been lost by evaporation and by transference from flask to still. The final separation of methyl and ethyl acetates and of ethyl and propyl acetates was carried out in the manner described for the later fractionations of mixtures of benzene and toluene, but it was necessary to treat the methyl acetate with phosphorus pentoxide to remove moisture, and the propyl acetate with potassium carbonate to remove free acid due to slight hydrolysis. The loss was thus much greater than it would otherwise have been.

Table 41

The final results are given below.