What is the Difference Between Dimethylamine and Trimethylamine?

Dimethylamine and trimethylamine are both organic compounds with the general formula (CH3)xNH2, where x is the number of methyl groups attached to the amine group. The main differences between these two compounds are:

1. Number of methyl groups: Dimethylamine has two methyl groups attached to the amine group, while trimethylamine has three methyl groups attached to the same nitrogen atom.
2. Basicity: Dimethylamine is more basic than trimethylamine, with a pKb of 3.29, while trimethylamine has a pKb of 4.19. This difference in basicity can be attributed to the steric crowding of three methyl groups in trimethylamine, which hinders the nitrogen lone pair's availability, whereas dimethylamine's nitrogen lone pair is more available due to less crowding.
3. Chemical reactions: When mixed with Hinsberg's reagent, dimethylamine can produce N,N-dimethyl benzene, which is insoluble in an aqueous KOH solution because it has two methyl groups attached to the nitrogen. In contrast, trimethylamine does not react with this reagent because it has three methyl groups attached.
4. Physical properties: Dimethylamine has a density of 649.6 kg/m³, a melting point of -93°C, and a boiling point that ranges from 7-9°C. Trimethylamine has similar properties, but its boiling point is higher than that of dimethylamine. This difference in boiling points is due to the additional methyl group in trimethylamine, which increases the molecular weight and intramolecular hydrogen bonding, leading to higher boiling point.

Comparative Table: Dimethylamine vs Trimethylamine

Dimethylamine and trimethylamine are two important amine compounds used in various industrial and laboratory applications. Here is a table comparing their differences:

Dimethylamine has two methyl groups attached to the same nitrogen atom, while trimethylamine has three methyl groups attached to the same nitrogen atom. The density of dimethylamine is 649.6 kg/m³, and it has a melting point of -93°C and a boiling point ranging from 7-9°C. When dimethylamine is mixed with Hinsberg's reagent, it produces N,N-dimethyl benzene, which is insoluble in an aqueous KOH solution. Trimethylamine, on the other hand, does not react with Hinsberg's reagent. The boiling point of trimethylamine (3.5°C) is lower than that of its isomer 1-aminopropane (48.5°C).