Ammonium carbamate, reversible

Chitosan has been recently found to be soluble in alkaline media, viz. NH4HCO3 solutions, where it assumes the ammonium carbamate form Chit-NHC02 NH4, i.e., a transient anionic form that keeps it soluble at pH 9.6, while reversibly masking the polycationic nature of chitosan. Because ammonium carbamates and NH4HCO3 decompose thermally and liberate CO2, NH3 and water, this alkaline system is suitable for producing chitosan microspheres by spray-drying (Table 1) [206]. 

Solid ammonium carbamate is stored in a compartment above the proportioning unit. The sublimation of solid blocks of ammonium carbamate is achieved by a local heater (spray or electrically warmed oil circulation). The sublimation temperature of ammonium carbamate is 60°C. The process being reversible, solid ammonium carbamate may be formed back for temperature lower than 60°C. 

Carbamates Reversed-phase-C18, acetonitrile-water-ammonium acetate MS (thermospray) 0.025-1 ppm 121... 

Ammonium carbamates are readily and reversibly produced on reaction of secondary amines with carbon dioxide. In the presence of a ruthenium catalyst precursors such as Ru3(CO)12 [3], (arene)RuCl2(PR3) [4] or Ru(methallyl)2(dppe) [5] (dppe=bis(diphenylphosphino)ethane) complexes, the three-component combination of a secondary amine, a terminal alkyne, and carbon dioxide selectively provides vinylcarbamates resulting from addition of carbamate to the terminal carbon of the triple bond (Scheme 2). 

The most important example of the reactions in this section s title is the second reaction of the urea synthesis (B) (Figure 8.15). It starts from ammonium carbamate (A) generated in situ. In a reversible acid/base reaction, A—to a minor extent—is transformed into NH3 and the unsubstituted carbamic acid C. In a reversal of its formation reaction the latter decomposes—... 

Dynamic Capture of Carbon Dioxide via Reversible Ammonium Carbamate Formation... 

Fig. 11 (a) C02 capture by reversible ammonium carbamate formation, (b) Example of linear solid oligomer formed upon reaction of 2-hydroxy-l,3,5-benzenetrialdehyde and at least 3 equiv. of diethylenetriamine in the presence of C02... 

Carbon dioxide reacts with ammonia to give ammonium carbamate, a solid. The reverse reaction also occurs ... 

Distamine " penicillamine, distamycin A stallin dn. distigmine bromide [ban. inn, jan] (Ubretid ) is a bisquaternary ammonium carbamate, a reversible ANTICHOLINESTERASE. It is a PARASYMPATHOMIMETIC that can be used to stimulate the bladder to treat urinary retention, and the intestine to treat paralytic ileus. It can also be used to enhance neuromuscular transmission in the treatment of... 

George, M. and R.G. Weiss, Chemically reversible organogels via latent gelators. Aliphatic amines with carbon dioxide and their ammonium carbamates. Langmuir, 2002.18(19) 7124-7135. 

Xenobiotics which reduce plant growth without affecting the pattern of development have been available for almost 40 years. A group of nicotinium growth retardants was described by Mitchell et al. in 1949 [36], followed shortly by the quaternary ammonium carbamates, including AMO-1618 [47]. Partial reversal of the dwarfing effect of these compounds by GA3 [32] and the demonstration that the retardants reduced GA production by the fungus Fusarium moniliforme [30] implicated GA biosynthesis as a site of action. This was confirmed by Dennis et al. 

Ramachandran BR, Halpern AM, Glendening ED (1998) Kinetics and Mechanism of the Reversible Dissociation of Ammonium Carbamate Involvement of Carbamic Acid. J Phys Chem A 102(22) 3934-3941... 

Due to the incomplete second reaction, the reactor outlet mixture contains significant amounts of ammonium carbamate in addition to urea and water. The ammonium carbamate is usually removed by decomposing into its constituents ammonia and carbon dioxide (reverse reaction of Eq. (3.15)) via increasing temperature and decreasing pressure [12]. Stripping using ammonia or carbon dioxide also supports ammonia carbamate decomposition [12] (see also process description in Section 3.3.2) and, in addition, removes the formed ammonia and carbon dioxide from the hquid phase. 

R. Ehrenfeld found that the carbamate in commercial ammonium chloride is not reduced by hydrogen at the cathode during electrolysis. If the current be rapidly reversed during the electrolysis of soln. of commercial carbonate (containing carbamate), with platinum electrodes, E. Drechsel found after 8 hrs. a salt of a platinum base is contained in the soln. There is also formed in the first or oxidation state NH40.C0.NH2+0=H20+C02(NH2)2 and this undergoes a further... 

Based on features of their interaction with ChE, anti-cholinesterase substances are clas-sified as reversible and irreversible inhibitors. Referred to the reversible anti-cholinesterase substances are quaternary ammonium compounds and aminoformic acid esters OPC are referred to the irreversible anti-cholinest-erase substances. At the same time, a great amount of anti-cholinesterase substances, carbamates in particular, though induce transitional reversible inhibition of ChE, are irreversible reagents. They are destroyed on the enzyme surface. 

However, the RCM methodology has also several drawbacks. First, the basic amino group in the substrate, if present, deactivates the catalyst. Therefore, before the reaction, it should be reversibly masked as, for example, a carbamate, amide, or ammonium salt. Second, the metathesis catalysts are still very expensive - a fact, that cannot be ignored when planning the synthesis on a larger scale. Moreover, the pollution of the products with ruthenium, even many steps after the metathesis reaction. 

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