Simple condensation

The kinetics of this type of polymerization are the same as for simple condensation for this reason, the use of the term polycondensation is perhaps more appropriate. Unless kinetic evidence suggests otherwise, polymerizations involving the formation of chain polymers from cyclic compounds, following ring scission, are classed as condensation polymerizations. Some important con-... 

Discussion of ladder polymers also enables us to introduce a step-growth polymerization that deviates from the simple condensation reactions which we have described almost exclusively in this chapter. The Diels-Alder reaction is widely used in the synthesis of both ladder and semiladder polymers. In general, the Diels-Alder reaction occurs between a diene [XVI] and a dienophile [XVll] and yields an adduct with a ring structure [XVlll] ... 

N -Heterocyclic Sulfanilamides. The parent sulfanilamide is manufactured by the reaction of A/-acetylsulfanilyl chloride with excess concentrated aqueous ammonia, and hydrolysis of the product. Most heterocycHc amines are less reactive, and the condensation with the sulfonyl chloride is usually done in anhydrous media in the presence of an acid-binding agent. Use of anhydrous conditions avoids hydrolytic destmction of the sulfonyl chloride. The solvent and acid-binding functions are commonly filled by pyridine, or by mixtures of pyridine and acetone. Tertiary amines, such as triethylamine, may be substituted for pyridine. The majority of A/ -heterocycHc sulfanilamides are made by simple condensation with A/-acetylsulfanilyl chloride and hydrolysis. 

In order to expand the utility of the reaction, modification of the route to anilidomethylene malonic ester equivalents was developed. Simple condensation of triethyl orthoformate with cyanoacetic ester, acetoacetic ester, or malonic ester in the... 

Besides simple condensation reactions, valence isomerization reactions, in particular, arc used for the synthesis of unsaturated, eight-membered-ring azaheterocycles. These isomeriz-ations mainly involve rearrangements of nitrogen-containing bicyclo[4.2.0]octatriene or semi-bullvalene systems. 

If the ketone group comes from a nitro group, a Diels-Alder disconnection is possible to give a simple condensation product (27), from nltromcthane and aldehyde (28). 

The synthesis of a local anaesthetic required amino lactone (56) as intermediate. The amino groups could be made from a ketone, but if we use a nitro group instead (57) a reverse Michael disconnection gives a simple condensation product (58). 

Polylactic acid (PLA) has been produced for many years as a high-value material for use in medical applications such as dissolvable stitches and controlled release devices, because of the high production costs. The very low toxicity and biodegradability within the body made PLA the polymer of choice for such applications. In theory PLA should be relatively simple to produce by simple condensation polymerization of lactic acid. Unfortunately, in practice, a competing depolymerization process takes place to produce the cyclic lactide (Scheme 6.10). As the degree of polymerization increases the rate slows down until the rates of depolymerization and polymerization are the same. This equilibrium is achieved before commercially useful molecular weights of PLA have been formed. 

The ditetrazolide of methylphosphite plays a role in the solid phase synthesis of polynucleotides. The ditetrazolide, which is stable for weeks when stored at —20 °C, is prepared in a simple condensation reaction between methylphosphordichloridite and two equivalents of tetrazole in anhydrous tetrahydrofuran in the presence of 2,4,6-tri-methylpyridine.t28]... 

A simple condenser is another possible alternative for treating exiting vapors. This alternative is particularly attractive if the vapors have a relatively high boiling point and if the recovered condensate is valuable. This alternative should always be evaluated because it is simple and usually less expensive and because it minimizes the volume of material that may need additional post-treatment. The design of condenser systems is covered by Kern.12... 

The heteroatom version of the vinylcyclopropane rearrangement serves to facilitate alkaloid construction. Scheme 13 outlines a strategy for the pyrrolizidine alkaloid isoretronecanol 211 90). Use of a carboxaldehyde (i.e. 213) as a synthon for the primary alcohol provides an ability to adjust stereochemistry. It also sets up formation of the pyrrolidine ring bearing the aldehyde by an aldol-type condensation of an enol of the aldehyde onto an imine derived from 214. Because of the lability of such systems, introduction of X=PhS imparts stability. The resultant azacyclopentene translates to an imine 215 using the iminocyclopropane rearrangement methodology. Simple condensation of the primary amine 216 with aldehyde 37a then initiates this... 

Sarvari has prepared a number of aldoximes using ZnO/CHsCOCl (Scheme 4). It was carried out by simple condensation between hydroxylamine hydrochloride and the desired aldehyde in the presence of zinc oxide (ZnO) as catalyst at 60 °C for a few minutes. 

To illustrate how a (simple) condensation calculation works, let s consider the condensation of corundum (Al203), one of the earliest phases predicted to condense from a solar gas. The partial pressures of aluminum (PAi) and oxygen (P0) in the gas phase must first be determined, based on their solar abundances, over a range of temperatures. The eguilibrium between solid (s) corundum and gas (g) can be represented by this equation ... 

Only one compound can enolise, and the diketone will act as the electrophilic component as it is more reactive than a mono ketone. We begin with a simple condensation ... 

Some of the simple condensations of a-ketoesters with a-halogenoketones suffer from the disadvantage that mixtures of furans may result. Nakanishi used this reaction in condensing chloroacetaldehyde with ethyl acetoacetate in the presence of pyridine to give the known 2-methyl-3-furoate in 55% yield during the synthesis of an insecticide (70MI31200). 

The versatility of 5-nitrosopyrimidines in pteridine syntheses was noticed by Pachter (64MI21603) during modification of the Timmis condensation between (262) and benzyl methyl ketone simple condensation leads to 4-amino-7-methyl-2,6-diphenylpteridine (264) but in the presence of cyanide ion 4,7-diamino-2,6-diphenylpteridine (265) is formed (equation 90). The mechanism of this reaction is still uncertain (63JOC1187) it may involve an oxidation of an intermediate hydroxylamine derivative, nitrone formation similar to the Krohnke reaction, or nucleophilic addition of the cyanide ion to the Schiff s base function (266) followed by cyclization to a 7-amino-5,6-dihydropteridine derivative (267), oxidation to a quinonoid-type product (268) and loss of the acyl group (equation 91). Extension of these principles to a-aryl- and a-alkyl-acetoacetonitriles omits the oxidation step and gives higher yields, and forms 6-alkyl-7-aminopteridines, which cannot be obtained directly from simple aliphatic ketones. 

The simple condensation between two amino-acids to form one molecule yields a dipeptide. Polypeptides are thus large molecules of amino-acids linked together via peptide bonds. 

In some organisms sulfur incorporation involves homocysteine as an intermediate. In such cases cysteine formation occurs by a transsulfuration reaction, with the intermediate formation of L,L-cystathionine (fig. 21.86). Cystathionine is formed in a simple condensation reaction from serine and homocysteine by cystathionine-jS synthase. 

If R1 and/or R2 are hydrogen the selectivity drops nearly to zero. The transformation can also be performed in a two-step mode. Thus, imine 235 could be prepared by simple condensation of 233 and 234 in the presence of molecular sieves, and this then cyclized in the presence of SnCl4. 

A number of early homogeneous membranes were made by simple condensation reactions of suitable monomers, such as phenol-formaldehyde condensation reactions of the type ... 

When maleic anhydride is used as the dipolarophile, simple condensation occurs with benzothiazole giving a hve-membered cycloadduct as a mixture of cis and trans... 

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