Ureas reactions

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 substituted urea reaction is shown as the second item of Fig. 1. The reaction of an amine and an isocyanate is quite rapid at room temperature and often does... 

Oligomeric methylols, whieh have not reacted further in the aeid eondensation reaction or which have been formed by the above-mentioned post-added urea reaction... 

The preparation of derivatives of this ring system has also been achieved by reaction of substituted piperazines with urea. Reaction of the starting piperazinone (284) with urea under fusion conditions gives the desired ring system (285) (66CPB194). 

In the second manufacturing process for copper phthalocyanine, phthalonitrile, copper(II) acetate and ammonium acetate are heated in the presence of a base, with or without a solvent such as pyridine. The mechanism of this has been less studied than that of the phthalic anhydride/urea reaction. It is, however, significant that metal-free phthalocyanine is manufactured by heating phthalonitrile with the sodium derivative of a high-boiling alcohol in an excess of the alcohol. This reaction is believed148 to occur by the route outlined in Scheme 7, which is supported by the isolation of compounds of types (223) and (224). If this or a related mechanism operates in the... 

Alternately, the importance of the hemiacetal group can be studied by using a compound that is an analog for a monosaccharide without the rest of the hydroxyl groups. Tetrahydro-2H-pyran-2-ol (THP) is such an analog for xylose. THP was reacted with an equimolar amount of DMU, in the absence of phenol, to follow the course of the hemiacetal-urea reactions. The acid-catalyzed mixture was heated between 81 and 116 °C over a 2-hour period. Samples were frozen to prevent further reaction prior to analysis. 

Tertiary aliphatic isocyanates can be made by addition of isocyanic acid (a toxic material) to olefins (2.17). Cytec (formerly American Cyanamid) makes a diisocyanate this way.58 The reaction can be controlled to produce the monoadduct which can be used as a monomer. Tertiary isocyanates of this type react at lower rates than primary ones in addition reactions. The isocyanic acid can be produced by the pyrolysis of cyanuric acid which, in turn, can be prepared from the urea (reaction 2.18). 

Pyrimido[5.4-r/]pyrimidines 5 and 6 are readily prepared by the condensation of 5-amino-2,6-dihydroxypyrimidine-4-carboxylic acid ( orotic acid ) with formamidc or urea. Reaction of the starting pyrimidine with formamide gives pyrimido[5,4-c/]pyrimidine-2,4,8-triol (5), which can also be prepared from ethyl 5-aminoorotate in 72% yield. In this case, the 5-amino group is first converted into the (ethoxymethylene)amino derivative and then treated with ammonia.207 The corresponding tetrol 6 results from reaction of the starting pyrimidine with urea.152,203... 

Polyureas (8). Many synthetic methods for preparation of polyureas are known. Examples of reactions that can be used for the preparation of a variety of polyurea structures include reaction of diamines with phosgene (Reaction 21), with urea (Reaction 22) or with diisocyanates (Reaction 23). 

The polyurethanes, although not used in large volumes, have specific applications of value for aerospace. Accordingly, a brief discussion of the chemistry and the material applications is in order. There are three chemical reactions of importance the reaction of hydroxyl groups with isocyanates to form urethanes (Reaction 1), the reaction of isocyanates with water to form amines (Reaction 2), and the reaction of amines with isocyanates to form ureas (Reaction 3). 

Source K. V. Gopalan, Study of Urea-Reaction for Dewaxing of Washed Blue Oil from Indian Crude Oil, Proceedings of the 4th World Petroleum Congress, vol. V, Section IIIB, Paper 6, pp. 155-167 (1955). With permission. 

Pig feed - Concentration Drying (singly or with other materials) Crystallization to cattle lick ANIMA Reaction with urea Reaction to give ammonium lactate Biomass L USE... 

The minor part of the CO, entering the synthesis as a feed, enters the urea reactor at the bottom in order to produce sufficient heat for the endothermic urea reaction. 

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