Ureas basicity

In the hands of Collie and Tickle in 1899 this reaction gave the first crystalline pyrylium salts. The salt character of the compounds was proved by conductivity measurements the basicity of 2,6-dimethylpyrone was found to be a little higher than that of urea. Basicities of other pyrones decrease in the order 2,6-dimethyl-> 2-phenyl-6-methyl-> 2,6-diphenylpyrone, paralleling the dipole moments. These hydroxypyrylium salts hydrolyze in water to pyrones. " The formation of salts of 2,6-dimethylpyrone with organic acids was investigated by Kendall,and with mineral acids by Cook. 11 ... 

Temp.3 C Method A (Urea-Basic Sulfate Method) 1%) Method B (Urea-Basic Succinate Method) (%) Method C lUrea Method)b (%) Method D (Ammonium Hydroxide Method) (%)... 

Cu/SiOj Urea Basic Cu nitrate (Cu2(0H)3N03) or Cu phyllosilicate 9 ... 

Urea oxalate is also sparingly soluble in amyl alcohol and since urea is soluble in this alcohol, the property may be utilised in separating urea from mixtures. An aqueous extract of the mixture is rendered slightly alkaline with sodium hydroxide solution and extracted with ether this removes all the basic components, but not urea. The residual aqueous solution is extracted with amyl alcohol (to remove the urea) upon adding this extract to a solution of oxalic acid in amyl alcohol crystalline urea oxalate is precipitated. 

Anion-exchange resins contain a basic radical, such as —NH and =NH, and are prepared by the condensation of formaldehj de with amines such as m-phenylenediainine and urea. These resins can absorb acids by the formation of salts, —NH3CI and =NHjCl, and are regenerated by treatment with sodium hydroxide or sodium carbonate. 

The nucleophilicity of the nitrogen atom survives in many different functional groups, although its basicity may be lost. Reactions of non-basic, but nucleophilic urea nitrogens provide, for example, an easy entry to sleeping-pills (barbiturates) as well as to stimulants (caffeine). The nitrogen atoms of imidazoles and indole anions are also nucleophilic and the NH protons can be easily substituted. 

Urea resin adhesives, by the use of the proper hardener, may be set either by heat or at room temperature. For room temperature curing, the hardener may be ammonium chloride, together with basic materials like calcium phosphate to neutralize excess acid that might damage the wood. Cold set or room temperature set adhesives are those that set satisfactorily at 20 —30°C, whereas a hot set adhesive generally means one that is set above 99 °C. 

Ammonia and nitric acid are the two basic ingredients in the manufacture of ammonium nitrate. In addition to consuming ammonia directly, the manufacture of ammonium nitrate consumes ammonia by way of nitric acid production. The largest single use of nitric acid is that of ammonium nitrate production (see Ammonium compounds). Urea (qv) is manufactured by reacting ammonia and carbon dioxide. Urea manufacturing faciHties are often located close to ammonia plants. 

Synthetic chemical approaches to the preparation of carbon-14 labeled materials iavolve a number of basic building blocks prepared from barium [ CJ-carbonate (2). These are carbon [ C]-dioxide [ CJ-acetjlene [U— C]-ben2ene, where U = uniformly labeled [1- and 2- C]-sodium acetate, [ C]-methyl iodide, [ C]-methanol, sodium [ C]-cyanide, and [ CJ-urea. Many compHcated radiotracers are synthesized from these materials. Some examples are [l- C]-8,ll,14-eicosatrienoic acid [3435-80-1] inoxn. [ CJ-carbon dioxide, [ting-U— C]-phenyhsothiocyanate [77590-93-3] ftom [ " CJ-acetjlene, [7- " C]-norepinephrine [18155-53-8] from [l- " C]-acetic acid, [4- " C]-cholesterol [1976-77-8] from [ " CJ-methyl iodide, [l- " C]-glucose [4005-41-8] from sodium [ " C]-cyanide, and [2- " C]-uracil [626-07-3] [27017-27-2] from [ " C]-urea. All syntheses of the basic radioactive building blocks have been described (4). 

There was a tendency to use these resins mixed with urea—formaldehyde or melamine-type resins. Preparation of pure tria2ones or uron resins is difficult and expensive (61,62). Furthermore, the basic nature of the amine nitrogen in tria2one permits the use of mixtures of tria2ones with other agents to yield finishes that retain strength in hypochlorite bleaching. 

Diazophenols, ie, o-hydroxyaryldiazonium salts, couple to 1-naphthol in weaMy basic solution primarily in the para position, but as the hydroxyl ion concentration is increased, formation of the ortho isomer is favored and is frequentiy the sole product. Pyridine and pyridine derivatives, urea, and acetate, etc, used as buffers can also catalyze azo coupling reactions (28). l-amino-2-naphthol-4-sulfonic acid [116-63-2] (1,2,4-acid) and 1-naphthol yield the important Eriochrome Black A [3564-14-5] (18a, R = H) (Cl Mordant Black 3 Cl 14640) which is reportedly (20) a mixture of ortho and para isomers. 

These compounds are stable only under basic conditions and must be held at high pH if stored for considerable periods of time. In Step 2, these methylolureas further react under acidic conditions with urea to form the various methylene urea oligomers. Water generated from the condensation reaction is removed by evaporation when producing granular UE products. 

A number of products are being marketed under the trade name POLYON. These include coated basic fertilizer materials, ie, urea, potassium nitrate, potassium sulfate, potassium chloride, ammonium sulfate, ammonium phosphate, and iron sulfate, in various particle sizes. Coatings weights on urea vary from 1.5 to 15%, depending on the release duration desired. Table 6 Hsts typical products. 

Propargyl alcohol (332) and (328) react readily with isocyanates in the presence of a basic catalyst to give 4-methylene-2-oxazolidinones (334) and 4-methylene-2-imidazolinones (336), respectively (63JOC991). In the absence of sodium methoxide the intermediate methanes (333) and ureas (335) were obtained and on treatment with sodium methoxide underwent ring closure. Moderate to excellent yields were obtained. 

Modification of urea resins with certain organic bases, e.g. triethylene-tetramine, will give resins with basic groups which form ionisable salts in the presence of acids ... 

Both the wood-based panel industry and the adhesive industry show a high commitment to and great capability towards innovation. The best evidence for this is the considerable diversity of types of adhesives used for the production of wood-based panels. Well-known basic chemicals have been used for a long time for the production of the adhesives and their resins, the most important ones being formaldehyde, urea, melamine, phenol, resorcinol and isocyanate. The greater portion of the currently used adhesive resins and adhesives for wood-based panels is produced with these few raw materials. The how to cook the resins and the how to formulate the adhesive become more and more complicated and sophisticated and are key factors to meet today s requirements of the wood-based panel industry. 

Despite the fact that the two main components of UF-resins are urea and formaldehyde, a broad variety of possible reactions and structures in the resins can be obtained. At the molecular level, the basic characteristics of UF-resins can be explained as follows (1) high reactivity (2) water solubility and dispersibility, which renders the resins ideal for use in the woodworking industry and (3) the reversibility of the aminomethylene link, which also explains the low resistance of the UF-resins against the influence of water and moisture, especially at higher temperatures. This is also one of the reasons for the subsequent formaldehyde emission. 

The reaction of urea and formaldehyde to form UF-resins is basically a two-step process, usually an alkaline methylolation followed by an acidic condensation. 

In the literature, various other types of resin preparation procedures are described, e.g. yielding uron structures [20-22] or triazinone rings in the resins [23,24]. The last ones are formed by the reaction of urea and an excess of formaldehyde under basic conditions in the presence of ammonia or an amine, respectively. These resins are used to enhance the wet strength of paper. 

Aminos. There are two basic types of amino plastics - urea formaldehyde and melamine formaldehyde. They are hard, rigid materials with good abrasion resistance and their mechanical characteristics are sufficiently good for continuous use at moderate temperatures (up to 100°C). Urea formaldehyde is relatively inexpensive but moisture absorption can result in poor dimensional stability. It is generally used for bottle caps, electrical switches, plugs, utensil handles and trays. Melamine formaldehyde has lower water absorption and improved temperature and chemical resistance. It is typically used for tableware, laminated worktops and electrical fittings. 

Gaseous CO2 is extensively used to carbonate soft drinks and this use alone accounts for 20% of production. Other quasi-chemical applications are its use as a gas purge, as an inert protective gas for welding, and for the neutralization of caustic and alkaline waste waters. Small amounts are also used in the manufacture of sodium salicylate, basic lead carbonate ( white lead ), and various carbonates such as M2CO3 and M HC03 (M = Na, K, NH4, etc.). One of the most important uses of CO2 is to manufacture urea via ammonium carbamate ... 

Methylation of nitrogen at the 2 position also proves to be consistent with diuretic activity. Condensation of 160 with urea affords the heterocycle, 193. Treatment of this compound with methyl iodide and base effects alkylation on the more acidic ring nitrogen (194). Basic hydrolysis then gives the N-methylated aminosulfonamide (195). Condensation of this with chloroacetalde-... 

The antiarrhythmic activity of local anesthetics has been noted several times previously. Another such agent is prepared by first alkylating isopropylamine with sulfone 199. Reaction of the ])ioduct (200) with diethylethylenediamine and carbonyldiimidazole results in transfer of the CDI carbonyl group and formation of the urea suricainide (201) [52]. The transform in all likelihood involves stepwise replacement of the imidazole groups by the basic groups in the other reactants. 

Hydroxides and basic salts. The necessity for careful control of the pH has long been recognised. This is accomplished by making use of the hydrolysis of urea, which decomposes into ammonia and carbon dioxide as follows ... 

Urea possesses negligible basic properties (Kb = 1.5 x 10 l4), is soluble in water and its hydrolysis rate can be easily controlled. It hydrolyses rapidly at 90-100 °C, and hydrolysis can be quickly terminated at a desired pH by cooling the reaction mixture to room temperature. The use of a hydrolytic reagent alone does not result in the formation of a compact precipitate the physical character of the precipitate will be very much affected by the presence of certain anions. Thus in the precipitation of aluminium by the urea process, a dense precipitate is obtained in the presence of succinate, sulphate, formate, oxalate, and benzoate ions, but not in the presence of chloride, chlorate, perchlorate, nitrate, sulphate, chromate, and acetate ions. The preferred anion for the precipitation of aluminium is succinate. It would appear that the main function of the suitable anion is the formation of a basic salt which seems responsible for the production of a compact precipitate. The pH of the initial solution must be appropriately adjusted. 

Determination of iron as iron (III) oxide by initial formation of basic iron (III) formate Discussion. The precipitation of iron as iron(III) hydroxide by ammonia solution yields a gelatinous precipitate which is rather difficult to wash and to filter. Iron(III) can, however, be precipitated from homogeneous solution as a dense basic formate by the urea hydrolysis method. The precipitate obtained is more readily filtered and washed and adsorbs fewer impurities than that formed by other hydrolytic procedures. Ignition yields iron(III) oxide. 

The pH at which basic iron(III) formate begins to precipitate depends upon several factors, which include the initial iron and chloride concentration a high concentration of ammonium chloride is essential to prevent colloid formation. It is important to use an optimum initial pH to avoid a large excess of free acid, which would have to be neutralised by urea hydrolysis, and yet there must be present sufficient acid to prevent the formation of a gelatinous precipitate prior to boiling the solution ideally, a turbidity should appear about 5-10 minutes... 

The synthesis of 2-substituted pyrimidines from 1,3-dicarbonyl compounds and urea derivatives was first described by Evans2 and was later improved by Hunt, McOmie, and Sayer3 for the preparation of 2-mercapto-4,6-dimethylpyrimidine. Burness4 employed 3-ketobutyraldehyde acetal in this procedure to give 2-mercapto-4-methylpyrimidine. 2-Mercaptopyrimidine has been prepared from 1,1,3,3-tetraethoxypropane and thiourea by variations of this basic method 3 6 6 as well as by the reaction of 2-chloropyrimidine with thiourea 1 or sodium hydrosulfide.8... 

These reactions can be opened up to all substances that can yield aniline derivatives in acid or basic medium. Carbamic acid derivatives, numerous variations of which are used as plant treatment agents, provide a striking application. As do urea herbicides and a variety of drug substances e. g. benzodiazepines or phenylbutazone derivatives. 

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