Low molecular weight chemicals are chemicals with a molecular weight less than 900Da and make up 90% of pharmaceutical drugs. They also include biological molecules such as fatty acids, glucose, amino acids and secondary metabolites such as lipids, glycosides, and alkaloids. And low molecular weight chemicals involve low molecular alcohols, acids and esters which can be used in all areas of human life and industrial production.
Understanding the basic chemical reactions of low molecular weight alcohols, Acids, Esters is helpful to master their properties and applications.
Fig. 1 The structure of alcohol
Alcohols, like water, are both weak bases and weak acids. The acid ionization constant (Ka) of ethanol is about 10-18, slightly less than that of water. Ethanol can be converted to its conjugate base by the conjugate base of a weaker acid such as ammonia (Ka~10-35), or hydrogen (Ka~10-38).
It is convenient to employ sodium metal or sodium hydride, which react vigorously but controllably with alcohols:
Alcohols are bases similar in strength to water and accept protons from strong acids. An example is the reaction of methanol with hydrogen bromide to give methyloxonium bromide, which is analogous to the formation of hydroxonium bromide with hydrogen bromide and water:
The OH group is not a good leaving group in nucleophilic substitution reactions, so neutral alcohols do not react in such reactions. However, if the oxygen is first protonated to give R−OH2+, the leaving group (water) is much more stable, and the nucleophilic substitution can take place. For instance, tertiary alcohols react with hydrochloric acid to produce tertiary alkyl halides, where the hydroxyl group is replaced by a chlorine atom by unimolecular nucleophilic substitution.
Most of the reactions of carboxylic acids belong to one of four principal classes, depending on the point in the molecule where the reaction occurs.
Fig. 2 The structure of acid
These include acid dissociation and solvolytic reactions. For example:
Most of which involve attack by a nucleophile: Nu on the carbonyl carbon with subsequent cleavage of a C-O bond. Examples are esterification, acyl chloride formation, and reduction with hydrides. For example:
These are reactions in which the R-C bond is broken in such a way that CO2 is lost and R-H is formed. For example:
Substitutions for hydrogen or halogen at the 2-carbon are especially important. For example:
Esters are one of the more useful functional groups. Their low reactivity makes the easy to work with and they are stable enough to be used as a solvent in organic reactions (ex. ethyl acetate). Esters are still reactive enough to undergo hydrolysis to form carboxylic acids, alcoholysis, to form different esters, and aminolysis to form amides. Also, they can react with Grignard reagents to form 3°alcohols and hydride reagents to form 1°alcohols or aldehydes.
Fig. 3 Reactions of esters
Alfa Chemistry offers various of low molecular weight alcohols, acids, esters. You can search the CAS No. or the chemical name on our website. If the products your search are not on our website you can contact us for custom synthesis.