Carboxylic acids boiling points

Boiling Points Carboxylic acids boil at considerably higher temperatures than do alcohols, ketones, or aldehydes of similar molecular weights. For example, acetic acid (MW 60) boils at 118 °C, propan-l-ol (MW 60) boils at 97 °C, and propionaldehyde (MW 58) boils at 49 °C. 

Carboxylic acids are substances with high boiling points formic acid 101 °C, acetic acid 118 °C and propanoic acid 141 °C. This is the consequence of dimerization and the formation of molecular aggregates via hydrogen bonds. Even in the gas phase, the molecules can remain in dimeric form. 

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... 

Hydrogen bonding m carboxylic acids raises their melting points and boiling points above those of comparably constituted alkanes alcohols aldehydes and ketones... 

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. 

B.5 parts of 1 -azaphenothiazine carboxylic acid chloride and 14 parts of piperidino-ethoxy-ethanol were introduced into 100 parts of chlorobenzene and the mixture boiled under reflux for 5 minutes. After cooling off the precipitated hydrochloride salt of piperidino-ethoxy-ethanol was filtered off on a suction filter. Water was added to the filtrate and the pH thereof adjusted to 5 to 6 with dilute HCI. The aqueous phase was then removed, a caustic soda solution added thereto and then extracted with ether. The ethyl extract waswashed with water, then dried with potash and the ether distilled off. 9.4 parts of the piperidino-ethoxy-ethyi ester of 1 -azaphenothiazine carboxylic acid were obtained. This product was dissolved in 20 parts of isopropanol and the solution neutralized with isopropanolic HCI. The monohydrochloride which precipitated out after recrystallization from isopropanol had a melting point of 160°Cto 161°C. 

C) 6-(n)-Propyl-2-Pyridone-4-Carboxylic Acid The 64 grams of the product just obtained are treated with 500 cc of concentrated hydrochloric acid at boiling point. 40 grams of a product, having a melting point of 285°C, are obtained. 

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. 

Melting and boiling points Primary amides have much higher melting and boiling points than carboxylic acids. Many simple amides are solid at room temperature. 

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

Most 1,2,3-triazolecarboxylic acids lose carbon dioxide when heated above the melting point. These reactions are often useful for the preparation of simpler triazoles, for example, in the synthesis of 1-vinyl-triazoles by decarboxylation of the corresponding 4-carboxylic acids. 4,5-Dicarboxylic acids normally lose 2 moles of carbon dioxide on heating above the melting point this is so, for example, with the u-triazole and with the 1-benzyltriazole but l-phenyltriazole-4,5-dicarboxylic acid preferentially decarboxylates at the 5-position, giving the 4-carboxylic acid. 6-Methyl-l-phenyl-4-carboxylic acid is reported to be de-carboxylated slowly in boiling benzene. ... 

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.)... 

This method is called the Fischer esterification. It s a condensation reaction where the loss of a water molecule accompanies the joining of the alcohol portion to the acid portion. The acid gives up the OH and the alcohol gives up the H to make the water molecule. All steps in the mechanism are reversible (that is, it establishes an equilibrium), so removing the ester as soon as it forms is helpful. Removal of the ester is normally easy since esters typically have lower boiling points than alcohols and carboxylic acids. Figure 12-20 illustrates the mechanism for the acid-catalyzed formation of an ester by the reaction of an alcohol with a Ccirboxylic acid. 

The compositions consist of a heat-plastified mixture of an ethylene homopolymer or copolymer, about 3 to 30 pbw of an elastomer, a stability control agent, which is a partial ester of a long chain fatty acid with a polyol, higher allyl amine, fatty acid amide or olefinically unsaturated carboxylic acid copolymer, and a hydrocarbon blowing agent having from 1 to 6 carbon atoms and a boiling point between -175 and 50C. 

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... 

Atophan. In a 1 litre round-bottomed flask, equipped with a reflux condenser, place 25 g. (24 ml.) of purified benzaldehyde (Section IV,115), 22 g. of freshly-distilled pyruvic acid and 200 ml. of absolute ethyl alcohol. Heat the mixture to the boiling point on a water bath and add slowly, with frequent shaking, a solution of 23 g. (22-5 ml.) of pure aniline in 100 ml. of absolute ethyl alcohol. The addition usually occupies about 1 hour. Reflux the mixture on a water hath for 3 hours, and allow to stand overnight. Filter off the crude atophan (1) at the pump and wash the crystals with a little ether. Recrystallise from ethyl alcohol (about 20 ml. per gram). The yield of pure 2-phenylquinoline-4-carboxylic acid, m.p. 210°, is 30 g. 

The acid is heated just to its boiling point (200-205°) (Note. 3), when it decomposes with the evolution of furan and carbon dioxide. The small amounts of 2-furan-carboxylic acid... 

Furan is a colorless liquid, boiling point 32°C. insoluble in water, soluble in alcohol or ether. Furan vapor produces a green coloration on pine wood moistened with hydrochloric acid. Furan may he made from mucic acid. COOHtCHOHLCOOH. by dry distillation into pyromneie acid, C4H1O - COOH. and then heating the latter under pressure at 270 C. Furan derivatives arc known, namely, methyl, primary alcohol, aldehyde, carboxylic acid, in which the group attachment is at carbon number 2 ... 

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