Boiling point of carboxylic acid

The melting points and boiling points of carboxylic acids are higher than those of hydro carbons and oxygen containing organic compounds of comparable size and shape and indicate strong mtermolecular attractive forces... 

The melting and boiling points of carboxylic acids are much higher than would be expeeted on the basis of their molecular weights. The usual explanation is that they form weak intramolecular bonds. 

Are the boiling points of carboxylic acids higher or lower than the boiling points of alcohols Explain your answer. 

The boiling points of carboxylic acids are approximately 30-40 °C higher than those of hydrocarbons, alcohols, ethers, aldehydes and ketones of comparable molar mass. For example, ethyl alcohol boils at 78 °C and formic acid at 100.5 °C. 

At room temperature, the Cj to C7 carboxylic acids are liquids and acids with more than 7 carbons are solids. Boiling points of carboxylic acids increase with increasing molar mass. However there is no regular change in the melting points of carboxylic acids. Carboxylic acids with an even number of carbon atoms melt at higher temperatures than similar acids with an odd number of carbon atoms. 

The boiling points of carboxylic acids are high relative to other classes of compounds due to hydrogen bonding carboxylic acid molecules can hydrogen bond in two places and as a result often exist as dimers. Lower molecular weight carboxylic acids are water soluble. 

Pure ethanoic (acetic) acid is a liquid, at room temperature, and is referred to as glacial ethanoic acid. The melting and boiling points of carboxylic acids are relatively high because of hydrogen bonding. Pairs of carboxylic acids molecules link up to produce hydrogen bonded dimers ... 

Acid chlorides, acid anhydrides, esters, and tertiary amides are polar, but due to lack a hydrogen atom that is capable of participating in hydrogen bonding, they have lower boiling points than carboxylic acids or alcohols of similar molecular weight, and similar boiling points to comparable aldehydes and ketones. 

Low molecular weight carboxylic acids are liquids at room temperature. Those with higher molecular weights are waxy sohds. The boiling points of carboxyhc acids are much higher than compounds with the same molecular weight and similar structures. 

The DTA shows a small endotherm at 140 °C consistent with the boiling point of propanoic acid (141 C) however, the insignificant mass loss suggests that only traces of free acid remained in the sample. A second endotherm at 245 is accompanied by a sharp mass loss of 24 %. A third larger endothermic mass loss occurs at 330 °C. The carboxylate-alumoxanes prepared by Kimura et al (13) showed similar endothermic mass losses (220 - 260 and 300 - 500°C). However, in contrast to the carboxylate-alumoxanes prepared from boehmite the second endotherm occurred over a larger temperature range. The reasons for this difference are at present unclear. 

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. 

Physical properties of carboxylic acids and derivatives include solubility, melting point, boiling point, and a few other characteristics. In this section we examine each class and discuss the most important physical properties. (In the upcoming section Considering the Acidity of Carboxylic Acids, we discuss the most important chemical property of Ccirboxylic acids — acidity.)... 

Problem 16.3 Account for the following physical properties of carboxylic acids, (a) Only RCOOH s with five or fewer C s are soluble in water, but many with six or more C s dissolve in alcohols. (f>) Acetic acid in the vapor state has a molecular weight of 120 not 60. (c) Their boiling and melting points are higher than those of corresponding alcohols. M... 

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