Boiling points of esters

Fig. 5. Solubility coefficient at 30°C versus boiling point of ester in a low density polyethylene film (18). For unit conversion see equation 6.

Applications. Transesterifications via alcoholysis play a significant role in industry as well as in laboratory and in analytical chemistry. The reaction can be used to reduce the boiling point of esters by exchanging a long-chain alcohol group with a short one, eg, methanol, in the analysis of fats, oils, and waxes. For more details see References 7 and 68. A few examples are given below. 

In general, esters have sweet odors. For this reason, many are useful in perfumes or as flavorings. The boiling points of esters are similar to those of aldehydes and ketones of compcirable molar masses, which means that the boiling points cire lower than comparable alcohols. 

The lower members of the series of add-esters are colourless liquids with pleasant, fruit-like odours the higher members, as well as those of the aromatic adds, are crystallisable compounds. The boiling-points of esters containing alkyl residues of small molecular weights (CHj, C2H C3Hr) are lower than those of the corresponding adds the entrance of more complex alkyl residues raises the boiling-points ... 

Figure 13. Solubility Coefficient at 85 C vs Boiling Point of Esters in EVOH...

Figure 18. Solubility Coefficient at 30 C vs. Boiling Point of Ester in a LDPE Film...

Alcoholysis (ester interchange) is performed at atmospheric pressure near the boiling point of methanol in carbon steel equipment. Sodium methoxide [124-41 -4] CH ONa, the catalyst, can be prepared in the same reactor by reaction of methanol and metallic sodium, or it can be purchased in methanol solution. Usage is approximately 0.3—1.0 wt % of the triglyceride. 

Acetic ester, boiling-point Boiling-point of ketone formed Melting-point , ... 

Ej Ethyl 2-(n)-Propyl-lsonicotinate The product just obtained is dechlorinated by catalyti-cally hydrogenating it in an alcoholic medium in the presence of palladium black and potassium acetate. 30 grams of ester, having a boiling point of 121°-125°C/7 mm, are obtained. 

The liquid ester is an equilibrium mixture, the enol content of which is increased by distillation and falls slowly, on standing, to 30 per cent.1 The boiling point of i45-i47°/n mm., recorded in the literature, is higher than any noted in the present work. 

A third category of syn eliminations involves pyrolytic decomposition of esters with elimination of a carboxylic acid. The pyrolysis of acetate esters normally requires temperatures above 400° C and is usually a vapor phase reaction. In the laboratory this is done by using a glass tube in the heating zone of a small furnace. The vapors of the reactant are swept through the hot chamber by an inert gas and into a cold trap. Similar reactions occur with esters derived from long-chain acids. If the boiling point of the ester is above the decomposition temperature, the reaction can be carried out in the liquid phase, with distillation of the pyrolysis product. 

An example of solid-phase microwave synthesis where the use of open-vessel technology is essential is shown in Scheme 4.10. The transesterification of /3-keto esters with a supported alcohol (Wang resin) is carried out in 1,2-dichlorobenzene (DCB) as a solvent under controlled microwave heating conditions [22], The temperature is kept constant at 170 °C, ca. 10 degrees below the boiling point of the solvent, thereby allowing safe processing in the microwave cavity. In order to achieve full conversion to the desired resin-bound /3-keto ester, it is essential that the methanol formed can be removed from the equilibrium [22]. 

Dibenzyl ether no doubt forms the chief impurity in benzyl benzoate. Since the boiling-point of the former lies near that of the ester, it is not removed during the process of purification by distillation. 

The cooled reaction product is treated with 200 cc. of water, the layer of oil separated, washed once with a second portion of water, and subjected to distillation in vacuo. The first fraction of the distillate contains benzyl alcohol together with unchanged aldehyde, as well as a small quantity of water. The temperature then rises rapidly to the boiling-point of benzyl benzoate, when the receivers are changed. The product boils at 184-185°/15 mm., and analysis by saponification shows it to consist of 99 per cent ester. A yield of 410-420 g. is obtained, which corresponds to 90-93 per cent of the theoretical amount. This benzyl benzoate supercools readily, but after solidifying... 

Ethyl /3-bromopropionate may be prepared in the same manner in about 90 per cent yield. The boiling point of the ethyl ester is 77-79° at 19 mm. 

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