Condensation carbamate

With Stamicarbon s pool condenser technology, condensation can be done very efficiently by reversing the former high-pressure carbamate condenser s process and steam side. The entire heat exchanging part is submerged in condensed carbamate. This pool-type condensation enables higher heat transfer, while staging two-thirds of the entire synthesis section s urea conversion in its liquid holdup. Thus, the urea reactor... 

In a 250 ml. conical flask, fitted with an air condenser of wide bore, place 50 g. (51 -5 ml.) of acetonylacetone (see Section V,9, Note 2) and 100 g. of ammonium carbonate (lump form). Heat the mixture in an oil bath at 100° until effervescence stops (60-90 minutes) some ammonium carbonate (or carbamate) sublimes into the condenser and this must be pushed back into the reaction mixture by means of a stout glass rod. Replace the air condenser by a Liebig s condenser with wide bore inner tube and reflux the mixture gently (bath temperature, 115°) for a further 30 minutes dissolve the solid which has sublimed into the condenser in about 5 ml. of hot water and return the solution to the reaction mixture. 

In 1902, von Braun (76) showed that ammonium N-phenyldithio-carbamate condensed at low temperature to give ethyl N-phenyldithio-carbamylacetate (52) which, on heating, led to N-phenylrhodanine (53). 

The stripper off-gas going to the high pressure carbamate condensers also contains the carbamate recovered in the medium and low pressure recirculation sections. Both of these systems ate similar to those shown in the total-recycle process. 

The Stainicaibon process is described in Figures 3—7. The synthesis section of the plant consists of the reactor, stripper, high pressure carbamate condenser, and a high pressure reactor off-gas scmbber. In order to obtain a maximum urea yield pet pass through the reactor, a pressure of 14 MPa (140 bar) and a 2.95/1 NH —CO2 molar ratio is maintained. The reactor effluent is distributed over the stripper tubes (falling-film type shell and tube exchanger) and contacted by the CO2, countercurrendy. This causes the partial NH pressure to decrease and the carbamate to decompose. 

The urea solution out of the stripper bottom flows to a single-stage low pressure recirculation section (0.4 MPa, 4 bar). The stripper off-gas is sent to the carbamate condenser. 

In this condenser, part of the stripper off-gases are condensed (the heat of condensation is used to generate low pressure steam). The carbamate formed and noncondensed NH and CO2 are put into the reactor bottom and conversion of the carbamate into urea takes place. The reactor is sized to allow enough residence time for the reaction to approach equiUbrium. The heat required for the urea reaction and for heating the solution is suppHed by additional condensation of NH and CO2. The reactor which is lined with 316 L stainless steel, contains sieve trays to provide good contact between the gas and Hquid phases and to prevent back-mixing. The stripper tubes are 25-22-2 stainless steel. Some strippers are still in service after almost 30 years of operation. 

The carbamate solution from the scmbber flows to a high pressure ejector. The NH feed pressure induces enough head to convey the carbamate solution from the scmbber to the carbamate condenser. 

In 1994 Stamicarbon introduced a pool condenser in the synthesis section (see Figs. 4 and 5). This allowed a 34% decrease in reactor volume and a 45% decrease in carbamate heat-exchange area, thus reducing costs considerably for equipment, stmctural steel, and constmction. 

Toyo Engineering-AGES Process. The synthesis section of the ACES process (Fig. 8) consists of a reactor, a stripper, two carbamate condensers, a scmbber and operates at 17.5 MPa (175 bars). The reactor is operated at 190°C with a NH /CO2 ratio of 4.0 (mol/mol). Liquid NH is fed directly into the reactor by a centrifugal ammonia pump. Gaseous CO2 is sent from the centrifugal CO2 compressor to the bottom section of the falling-film type stripper. 

The stream from the reactor consisting of a mixture of urea, unconverted ammonium carbamate, excess water, and NH, is fed into the top of the stripper. The ACES stripper utilizes a ferrite—austenite stainless steel, as do the carbamate condensers. The reactor and scmbber are constmcted with 316 L urea-grade stainless steel. 

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). 

A. Ethyl N- p-tolylsulfonylmethyl)carhamate,[Carbamic acid, (4 -methyl-phenylsulfonylmethyl)-, ethyl ester]. A solution of 178 g. (1.0 mole) of sodium p-toluenesulfinate (Note 1) in 1 1. of water is placed in a 3-1., three-necked daak, equipped with a condenser, an efficient mechanical stirrer, and a thermometer. After addition of 100 ml. (108 g.) of a 34—37% solution of formaldehyde ca. 1.2-1.4 moles) (Note 2), 107 g. (1.2 moles) of ethyl carbamate (Note 3), and 250 ml. of formic acid (Note 4), the stirred solution is heated to 70°. Soon after this temperature is reached, the reaction mixture becomes turbid by separation of the... 

Indole-2,3-quinodimethanes have also been exploited as the key intermediates in indolo[2,3-a]caibazole synthesis, allowing the preparation of several interesting systems. Thus, when the starting materials 74a-b (obtained from the condensation of protected indole-2-carboxaldehydes with 2-aminostyrene) underwent treatment with methyl chloroformate in hot chlorobenzene, the carbamates 75a-b were obtained, and could subsequently be dehydrogenated into the aromatic compounds 76a-b (Scheme 11). However, all functionalization attempts of the methyl... 

Treatment of piperidine with nitrous acid affords the N-nitroso derivative (190) reduction gives the corresponding hydrazine (191). Condensation of this intermediate with the carbamate (192) obtained from p-toluenesulfonamide leads to the oral hypoglycemic agent tolazemide (193). In a similar vein, reaction of the hydrazine obtained by the same sequence from azepine (194) with the carbamate, 188, gives azepinamide (195). ... 

Thus, in one such example, hydroxyethylhydrazine (21) is first converted to the carbamate (22). Condensation with 18 yields nidroxyzone (23)... 

Reaction of hy - roffen cyanide with the a-iiydrazinoester, 34, leads to the carbamate (35). Cyclization by means of strong acid affords the corresponding aminohydantoin (36). Condensation with 18 affords nitrofurantoin (37). ... 

Where ammonia is employed to raise the condensate pH, several reactions take place, but none of the reaction products are particularly stable. Essentially, white ammonium carbamate is formed from the reaction of ammonia and carbon dioxide, and these damp feathery crystals may cause blockages in cold areas of the condensate system. The salt is unstable and, if heated, the ammonium carbamate forms urea [CCKNH ], which then hydrolyzes back to ammonia and carbon dioxide ... 

Bis(4-formylphenyl) succinate 2201 and octamethylene N,N -bis(trimethylsilyl) carbamate 2202 condense with aUyltrimethylsilane 82 in the presence of 10 mol% trityl perchlorate or TMSOTf 20 to give, after 24 h at 0°C in CH2CI2, the poly-... 

The reactor residence time is about 45 minutes, a 95 per cent approach to equilibrium being achieved in this time. The ammonia is fed directly to the reactor, but the carbon dioxide is fed to the reactor upwardly through a stripper, down which flows the product stream from the reactor. The carbon dioxide decomposes some of the carbamate in the product stream, and takes ammonia and water to a high-pressure condenser. The stripper is steam heated and operates at 180°C, whilst the high-pressure condenser is at 170°C and the heat released in it by recombination of ammonia and carbon dioxide to carbamate is used to raise steam. Additional recycled carbamate solution is added to the stream in the high-pressure condenser, and the combined flow goes to the reactor. 

The product stream leaving the stripper goes through an expansion valve to the low-pressure section, the operating pressure there being 5 bar. In a steam-heated rectifier, further ammonia and carbon dioxide are removed and, with some water vapour, are condensed to give a weak carbamate solution. This is pumped back to the high-pressure condenser. 

Quinazolines 51 have been prepared by the condensation of A-aryl carbamates with hexamine, followed by aromatisation of the dihydro intermediate. A variety of mono- and di-substituted anilides were used, mefa-substituted starting materials giving 7-substituted quinazolines <06T12351>. Benzoquinazolines were also prepared similarly from naphthylamine carbamates <06OL255>. 

In contrast to the Michaelis-Arbuzov reaction, triaryl phosphites prove to be quite useful for addition to a,(3-unsaturated carbonyl compounds in this type of reaction. A wide variety of unsaturated compounds have been utilized successfully as substrates for such additions, including condensation products of the simple carbonyl compounds with urea,229 thiourea,230-233 N-substituted thioureas,232 234 235 ethyl carbamate,236 2-imidazolidinone,237 2-imidazoli-dinethione,237 and benzyl carbamate.238-240... 

The situation with 7V-acyloxy-/V-alkoxyureas and carbamates is similar although infrared data were mostly determined by liquid film or condensed phase (KBr/nujol mull).52,131 However, the limited data for V-acyloxy-TV-alkoxyureas (Table 2, entries 69-72) give amide carbonyl frequencies ca. 1730 cm-1 that are raised by some 37-40 cm-1 by acyloxylation. Values for carbamates (Table 2, entries 73-77) are higher (mostly 1780 cm-1) but are raised to a lesser extent (10-20 cm-1) relative to their parent carbamates. Clearly, carbonyl vibrational frequencies will be influenced strongly by the adjacent amino or alkoxyl group in both analogues. 

The first reported synthesis of hydroxyurea (24) consists of the condensation of hy-droxylamine with potassium cyanate (Scheme 7.14) [87]. Condensation of hydroxy-lamine with ethyl carbamate also gives pure hydroxyurea in good yield after recrystallization (Scheme 7.14) [88]. Nitrogen-15 labeled hydroxyurea provides a useful tool for studying the NO-producing reactions of hydroxyurea and can be prepared by the condensation of N-15 labeled hydroxylamine with either potassium cyanate or trimethylsilyl isocyanate followed by silyl group removal (Scheme 7.14) [89, 90]. Addition of hydroxylamine to alkyl or aryl isocyanates yields alkyl or aryl N-hydroxyureas (Scheme 7.14) [91, 92]. The condensation of amines with aromatic N-hydroxy carbamates also produces N-substituted N-hydroxyureas (Scheme 7.14) [93]. 

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