Carbamates, reaction with

There are numerous advantages to this approach in addition to avoiding complex purification procedures. For instance, it is now possible to further diversify the nitrogen substituent of the reagent, which has a profound impact on the practicality of C—H amination. In 2001, Du Bois and Espino first reported the intramolecular C—H insertion reaction with carbamates and diacetoxyiodobenzene in the presence of rhodium (II) acetate or rhodium (II) triphenylacetate dimer and magnesium oxide [33]. The corresponding oxazolidinone was isolated in high yields (Eq. (5.4)). 

As the amine reacts again with isocyanate, this reaction will lead to branching, as will consecutive reactions with carbamates, leading to allophanates 6 (Scheme 3.23) and with ureas, leading to biurets 7 (Scheme 3.24). 

This approach is compHcated by the fact that the isocyanate is produced via the thermolytic cleavage of the methyl carbamate. Reactions with the unconverted carbamate caimot be prevented. Much effort has been focused on improving the selectivity of the latter step. 

Reaction with Acids. Under anliydrous conditions, mono- and diethanolamines and isopropanolaniines fomi carbamates with carbon dioxide (2,3). 

Another significant use of 3-methylphenol is in the production of herbicides and insecticides. 2-/ f2 -Butyl-5-methylphenol is converted to the dinitro acetate derivative, 2-/ f2 -butyl-5-methyl-4,6-dinitrophenyl acetate [2487-01 -6] which is used as both a pre- and postemergent herbicide to control broad leaf weeds (42). Carbamate derivatives of 3-methylphenol based compounds are used as insecticides. The condensation of 3-methylphenol with formaldehyde yields a curable phenoHc resin. Since 3-methylphenol is trifunctional with respect to its reaction with formaldehyde, it is possible to form a thermosetting resin by the reaction of a prepolymer with paraformaldehyde or other suitable formaldehyde sources. 3-Methylphenol is also used in the production of fragrances and flavors. It is reduced with hydrogen under nickel catalysis and the corresponding esters are used as synthetic musk (see Table 3). 

Multifunctional Hydroxy, Mercapto, and Amino Compounds. These are used to cross-link halogenated polymers. Depending on the labihty of the halogen, the cross-linking agents can be capped to reduce reactivity or used in combination with accelerators to increase the rate of reaction. Benzoyl capping is common with hydroxy and mercapto compounds forming the carbamate by reaction with one equivalent of carbon dioxide is used with diamines. 

Thorium compounds of anionic nitrogen-donating species such as [Th(NR2)4], where R = alkyl or sdyl, are weU-known. The nuclearity is highly dependent on the steric requirements of R. Amides are extremely reactive, readily undergoing protonation to form amines or insertion reactions with CO2, COS, CS2, and CSe2 to form carbamates. Tetravalent thorium thiocyanates have been isolated as hydrated species, eg, Th(NCS)4(H20)4 [17837-16-0] or as complex salts, eg, M4 Th(NCS)g] vvH20, where M = NH, Rb, or Cs. 

Reactions with Nitrogen Compounds. The reaction with ammonia is the classical method for preparing primary carbamates. Excess ammonia is used as an acid acceptor to remove the HCI formed (see Carbamic acid). 

Reaction with Amines and Ammonia. Carbonates react with amines and ammonia to produce carbamates or ureas. This reaction can be used as an alternative route to producing carbamate pesticides. 

Substitution on the phenethyl side chain of the substrate is usually well tolerated. For example, reaction of carbamate 44 with POCI3 afforded a 75% yield of the corresponding lactam 45. However, in some instances substituents on the chain lead to low yields, such as in the reaction of amide 46, which provided only a 29% yield of the desired product 47 (albeit with 9 1 diastereoselectivity). ... 

The most important group of derivatives for the amino function (Fig. 7-4) is the carbamate group, which can be formed by reactions with acids, acid chlorides or acid anhydrides. A series of chlorides as 2-chloroisovalerylchloride [1], chrysanthe-moylchloride [2] and especially chloride compounds of terpene derivatives (cam-phanic acid chloride [3], camphor-10-sulfonyl chloride [4]) are used. The a-methoxy-a-trifluoromethylphenylacetic acid or the corresponding acid chloride introduced by Mosher in the 1970s are very useful reagents for the derivatization of amines and alcohols [5]. 

The enantiomeric excess which is achieved for a given ally carbamate is independent of the carbonyl compound used it reflects the skill of the operator in the crystallization procedure. The high degree of reagent-controlled chirality transfer is also obvious from the reaction with either enantiomer of 2-benzyloxypropanal103a 107a. 

Ethyl carbamate, reaction with hydrox-ylamine to form hydroxyurea, 40, 60... 

Impurities in CL have also been destroyed by oxidation with ozone22 followed by distillation. Ozonation treatment of waste CL leaves no ionic impurities. However, the most commonly used oxidizing agents are potassium permanganate, perboric acid, perborate, and potassium bromate. Treatment of CL with these oxidizing agents is carried out in a neutral medium at 40-60°C. Strongly alkaline or acidic conditions accelerate the oxidation of CL to form isocyanates. Hie undesirable oxidation reaction is fast above pH 7 because of the reaction with isocyanate to form carbamic acid salts, which shifts the equilibrium to form additional isocyanate. 

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