Sciencemadness Discussion Board

Carbamate Synthesis

Chemichael - 12-1-2018 at 13:20

Here is a paper for synthesizing carbamates. Has anyone carried out this reaction before and what is the gas that escapes the system? It would be the procedure using tert-butyl alcohol in the first link. The boiling point for isocyanic acid is 23.5C, so I'm guessing it's not the gas. Is there isocyanic acid formed that can escape the system? Does the isocyanic acid hydrolyze into CO2 and ammonia?

They use DCM or benzene:

Here is another paper for the synthesis of carbamates without the use of solvents.

Edit by Moderator : Changed first link on request of OP

[Edited on 1-15-2018 by gdflp]

Dr.Bob - 12-1-2018 at 20:02

Not positive what causes the gas evolution, certainly any water in the alcohol will hydrolyze the isocyanic acid into CO2 and ammonia. Also t-butanol could eliminate water to form isobutylene in strong acid, not sure if that is fast enough to matter in this case. And carbamates can decompose to form ammonia and CO2 if the reaction gets too hot. Interesting way to make N-Boc-ammonia and other similar carbamates.

Chemichael - 13-1-2018 at 06:51

Thanks for the information.
Does anyone know if you can make a 68.62% solution of 34.3g of trichloroacetic acid in 50mL of dichloromethane? I would use a pressure equalized addition funnel if it does. I know they sell Deblock which is a 3% solution of trichloroacetic acid and dichloromethane, but not sure how much more soluble it is. I tried to find more information on the solubility without any luck.

Chemichael - 14-1-2018 at 17:04

Also if the admin could remove the first link I posted I would appreciate it, since I think you usually have to pay to see it.
I posted the procedure below instead. Thank you!

Tert-Butyl Carbamate
(2).-Trifluoroacetic acid (15.5 ml., 0.21 mole) was added (hood!) slowly to a stirred mixture of t-butyl alcohol (7.4g., 0.1 mole) and sodium cyanate (13 g., 0.2 mole) in 25-100 ml. of benze ne (volumes of solvent significantly larger than this decreased the yield). A mildly exothermic reaction occurred and some gas bubbled out of the system. The container was loosely stoppered, and the reaction mixture was stirred for 3 hr. (or overnight, the yield was the same). Fifteen milliliters of water was added and the organic layer was separated and dried: the solvent was removed in vucuo a t a pot temperature of 40-50 '. The residue solidified, 92% yield, m.p. 98-101 ', Recrystallization from water gave an analytically pure product, 8 g. (69%yield), m.p. 107-108" (lit.m.p. 108C).

[Edited on 15-1-2018 by Chemichael]

DJF90 - 15-1-2018 at 07:17

TFA and DCM are miscible in all proportions from personal experience.