Condensing agents

The early gas-phase reactors operated in the dry mode so that the heat of polymerization was removed only by the recycled gas stream which was passed through a heat exchanging unit and the cooler gas was ejected into the bottom of the reactor. At the time, a large UNIPOL reactor was designated as a G-5000 reactor where the 5000 denoted the volume of the reactor in cubic feet. The G-5000 contained about 100,000 pounds of fluidized granular polyethylene and a production rate of 25,000 to 40,000 lbs per hour was common, resulting in a catalyst residence time of 2.5-4.0 hours. 

Production of ethylene/1-hexene copolymers was limited by the reactivity of the catalyst with 1 -hexene. Ethylene partial pressure was therefore limited in order to remain in the dry mode and adjust the 1-hexene/ethylene molar ratio at the desired level to produce a LLDPE resin with a density of about 0.916 g/cc. 

The shorter start-up time for the smaller seed bed will also reduce the amoxmt of off-grade polyethylene produced, however, if the startup operation is carried out under the optimxim conditions where the process 

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In general, condensation takes place at the a-carbon atom, leading to simple cinnamic acids or to their a-substituted derivatives. When possible, the anhydride corresponding to the sodium sail should be the condensing agent. 

Ethyl acetoacetate may be prepared by the action of sodium upon dry ethyl acetate and decomposition of the resulting sodio compound with dilute acetic acid. Most samples of ethyl acetate contain some ethyl alcohol and it is usually assumed that sodium ethoxidc is the condensing agent ... 

The preparation of 4-methylcoumarin is an example of the Pechmann reaction, which consists in the interaction of a phenol with a 3-ketonic ester In the presence of a condensing agent (sulphuric acid, aluminium chloride, phosphorus oxychloride or pho.sphoric oxide) ... 

A simplified procedure is possible by using polyphosphoric acid as the condensing agent. Add 160 g. of polyphosphoric acid to a solution of 11 g. of resorcinol in 13 g. of ethyl acetoacetate. Stir the mixture and heat at 75-80° for 20 minutes, and then pour into ice-water. Collect the pale yellow solid by suction filtration, wash with a little cold water, and dry at 60°. The yield of crude 4-methyl-7-hydroxycoumarin, m.p. 178-181°, is 17 g. Recrystalbsation from dilute ethanol yields the pure, colourless compound, m.p. 185°. 

This reaction involves the condensation of an aldehyde or ketone with an a-halo ester in the presence of a basic condensing agent (sodium ethoxlde, sodamide, finely divided sodium or potassium iert.-butoxide) to give a glycldio (or ap-epoxy) ester. Thus acetophenone and ethyl chloroacetate yield phenyl-methylglycidic ester (I) ... 

The condensation of aldehydes and ketones with succinic esters in the presence of sodium ethoxide is known as the Stobbe condensation. The reaction with sodium ethoxide is comparatively slow and a httlo reduction of the ketonic compound to the carbinol usually occurs a shorter reaction time and a better yield is generally obtained with the more powerful condensing agent potassium ieri.-butoxide or with sodium hydride. Thus benzophenone condenses with diethyl succinate in the presence of potassium [Pg.919]

Simple esters (e.g., ethyl acetate) undergo the acetoacetic ester condense tion (compare Section 111,151). The effective condensing agent is sodium ethoxide, produced by the action of sodium upon traces of alcohol present in the ester ... 

A major problem in the development of phosphotriester syntheses has been the lack of appropriate condensing agents. DCC cannot be used, because it will not activate phosphodi-... 

With the dicyclohexylcarbodiimide (DCQ reagent racemization is more pronounced in polar solvents such as DMF than in CHjCl2, for example. An efficient method for reduction of racemization in coupling with DCC is to use additives such as N-hydroxysuccinimide or l-hydroxybenzotriazole. A possible explanation for this effect of nucleophilic additives is that they compete with the amino component for the acyl group to form active esters, which in turn reaa without racemization. There are some other condensation agents (e.g. 2-ethyl-7-hydroxybenz[d]isoxazolium and l-ethoxycarbonyl-2-ethoxy-l,2-dihydroquinoline) that have been found not to lead to significant racemization. They have, however, not been widely tested in peptide synthesis. 

A.lkylation of 2-sec-aminothiazoles can be directed to the amino group if condensing agents such as alkali amides are used (46j, This reaction is... 

With the more acidic 2-acetamido-4-R-thiazoles. using the weaker base NaOH as condensation agent, a mixture of ring (45) and exocyclic N-alkylation (46) may be observed (Scheme 33) (121). Reaction of 2-acetamido-4-methylthiazole in alcoholic sodium ethoxide solution with a variety of alkylating agents has been reported (40-44). 

By reaction of a corresponding quaternary salt in the presence of a condensation agent such as amyl nitrite or with a heterocycioammonium salt possessing a labile group, such as Cl, I. or SR (6. 11) in the 2-position, cyanine dyes are obtained (Scheme 52). 

Various 4-, 5-, or 4,5-disubstituted 2-aryIamino thiazoles (124), R, = QH4R with R = 0-, m-, or p-Me, HO C, Cl, Br, H N, NHAc, NR2, OH, OR, or OjN, were obtained by condensing the corresponding N-arylthiourea with chloroacetone (81, 86, 423), dichloroacetone (510, 618), phenacyichloride or its p-substituted methyl, f-butyl, n-dodecyl or undecyl (653), or 2-chlorocyclohexanone (653) (Method A) or with 2-butanone (423), acetophenone or its p-substituted derivatives (399, 439), ethyl acetate (400), ethyl acetyl propionate (621), a- or 3-unsaturated ketones (691), benzylidene acetone, furfurylidene acetone, and mesityl oxide in the presence of Btj or Ij as condensing agent (Method B) (Table 11-17). 

In organic chemistry, LiH serves as a condensation agent. In the presence of trialkyl boranes very powerful reducing agents, LiBHR, which are soluble in THF, are obtained. These materials reduce aUphatic haUdes and in some cases highly stereospecific reductions can be accompHshed. 

Symmetrical or unsymmetrical diacyl peroxides (20, R, R = alkyl or aryl) can be synthesi2ed directiy from carboxyhc acids and hydrogen peroxide or from peroxycarboxyhc acids with dicyclohexylcarbodiimide or A/,A/-dicarbonyldiimida2ole as condensing agents (187) ... 

Dicyclohexylcaibodiimide (43) [538-75-0] is an impoitant peptide-condensing agent and analytical reagent (86). 

The nitration bath normally contains sulphuric acid as a condensing agent and a typical bath for producing a cellulose nitrate with a nitrogen content of 11 % would be... 

Of special importance to the synthesis was the choice of condensing agents and cbnditions. HATU-HOAF was of particular value in these final stages. Condensation of the threonine carboxyl of 24 (from Scheme 5) with the pyrrolidine N s of the bisindolyl compound 15 (from Scheme 3) afforded 25. Removal... 

Wizinger and co-workers found that 2,6-diphenyl-4-pyrone or 4,0-diphenyl-2-pyrone react with A , Y-dimethylaniline in the presence of POCI3 and PCI 5, yielding triarylpyrylium salts 29 and 30, respectively. With the same condensing agents, the above authors reacted... 

Darzens claims a method in which a ketone is condensed with chloracetic-ether in the presence of an alkaline condensing agent. For example, acetone reacts with chloracetic-ether as follows —... 

This compound may be produced by reacting o-chlorobenzophenone with acetonitrile in the presence of sodium amide or another strongly basic condensing agent, to form the nitrile of /3-phenyl-/3-o-chlorophenyl-hydracrylic acid, which is then hydrogenated to yield Tphenyl-l-o-chlorophenyl-S-aminopropanol-l. The latter intermediate compound is subsequently dimethylated with an agent such as methyl sulfate to provide the desired end product l-o-chlorophenyl-Tphenyl-S-dimethylaminopropanol. 

The carboxyl terminated ACPA, 4,4 -azobis-(4-cya-nopentanoic acid), turned out to be a suitable reagent in condensation reactions. This compound can be prepared by Strecker s synthesis from levulinic acid following the method of Haines and Waters [12]. Regarding the formation of polymeric azo initiators, Matsakuwa et al. [13] reported on the condensation of ACPA with various diols and diamines in the presence of a condensation agent, I-methyl-2-chlorpyridinium iodide, and a cata-... 

Concerning the reaction of ACPC with diols, the frequent use of poly(ethylene glycol) has to be mentioned [20-24]. Ueda et al. ([22-24]) reacted preformed poly(ethylene glycol) (Mn between 6 x 10 to 2 x 10 ) with ACPC. In this case, unlike the reaction of ACPA with diols vide ante), no additional condensation agent was needed. The ethylene glycol-based thermally labile polymers were used to produce blocks with poly(vinyl chloride) [22], poly(styrene) [23], poly(methyl acrylate), poly(vinyl acetate), and poly(acrylonitrile) [24]. 

The bis-amino derivative of PDMS was polycon-densed directly with ACPA to give MAI by using 1,1 -dicarbonylimidazol as a condensation agent [15-18J. No formation of strong acid in this process will be acceptable for the plant. 

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