Self-condensation reaction

The replacement of the hydrogen of the methylo1 compound with an alkyl group renders the compound much more soluble in organic solvents and more stable. This reaction is also cataly2ed by acids and usually carried out in the presence of considerable excess alcohol to suppress the competing self-condensation reaction. After neutrali2ation of the acid catalyst, the excess alcohol may be stripped or left as a solvent for the amino resin. 

As is the case during manufacture, contact with those metallic impurities that catalyze Friedel-Crafts condensation reactions must be avoided. The self-condensation reaction is exothermic and the reaction can accelerate producing a rapid buildup of hydrogen chloride pressure in closed systems. 

The dimer acids [61788-89-4] 9- and 10-carboxystearic acids, and C-21 dicarboxylic acids are products resulting from three different reactions of C-18 unsaturated fatty acids. These reactions are, respectively, self-condensation, reaction with carbon monoxide followed by oxidation of the resulting 9- or 10-formylstearic acid (or, alternatively, by hydrocarboxylation of the unsaturated fatty acid), and Diels-Alder reaction with acryUc acid. The starting materials for these reactions have been almost exclusively tall oil fatty acids or, to a lesser degree, oleic acid, although other unsaturated fatty acid feedstocks can be used (see Carboxylic acids. Fatty acids from tall oil Tall oil). 

This has been attributed to the self-condensation reactions of these compounds,e.g., acetylacetaldehyde yields s-triacetylbenzene.° Hi. Ethoxymethylene compouTids. Ethoxymethyleneacetoacetates and ethoxymethyleneacetylacetones have been used to prepare pyrido[2,3-d]pyrimidines containing 6-ethoxycarbonyl or 6-acetyl... 

Tire condensation method (Section II,A,1) applied for 1,2,4-thiadia-zolium salts and phenylsubstituted imidazoles leads to the thia-tetraazaful-valenes 91 and 92 (70TL481). Moreover, 2,4,5-tris(ethylsulfanyl)imida-zolium chloride was converted to the unsymmetrical heterofulvalene 93 by a self-condensation reaction in the presence of potassium carbonate and elemental iodine (85PS223) (Scheme 37). 

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

The initial step of the polymerisation process is reaction of the amine groups with formaldehyde to generate methylol units, as illustrated in Reaction 1.9. Further heating of the polymer then leads to a variety of reactions. For example, the methylol groups can undergo self-condensation (Reaction 1.10). 

Example 13.3 The conversion of a self-condensing reaction can be limited to give polymers with finite lengths. How does the polydispersity of these polymers compare with those in Example 13.2 where the reaction went to completion with imperfect stoichiometry Make the comparison at the same average chain length. 

If the denominator in equation 12 is less than or equal to zero, the mixture has gelled. In this case, the weight average molecular weight is infinite. In the absence of the self-condensation reaction - 0), the gel point is given by ... 

Quinone methides (QMs), especially the simple ones (those not having substituents at the exocyclic methylene group), are very unstable compounds. Their isolation is very difficult and normally requires very dilute solutions and low temperatures.2 Due to the aromatic z witterionic form (Scheme 3.1), quinone methides react very rapidly with both electrophiles and nucleophiles, with the medium, or in self-condensation reactions. 

Likewise, the lactol 62, obtained by addition of methyllithium to 2,3,5-tri-O-benzyl-D-arabinono-1,4-lactone, underwent a self-condensation reaction in the presence of BF3 OEt2-MeCN, to afford an anomeric mixture of two C-disaccharides 63 and 64 in 93% yield (66). 

In 1899 R. C. Guerbet discovered the self-condensation reaction of alcohols, which, via the aldehyde as an intermediate, lead to branched structures (2-alkyl alcohols) (Fig. 4.21) - the Guerbet alcohols. Starting with fatty alcohols from vegetable sources, such as octanol and decanol, the corresponding C1(, and C2o alcohols are produced (2-hexyldecanol and 2-octyldecanol, respectively). The reaction is carried out under alkali catalysis and high temperatures (>200 °C). Over the years, both products have proven to be efficient emollients, but are also used for other applications, such as plasticizers or components for lubricants (Fig. 4.21). 

The methylol groups in reaction M12 can either deformylate (reaction M7) to amine or self condense (reaction M9) to yield melamine-melamine crosslinks. 

Self-condensations are another set of important reactions of organolithium compounds. Tamao and Kawachi had reported that [(tert-butoxy diphenyl)silyl]lithium (20) exhibited ambiphUic character, and underwent a self-condensation reaction to give a [2- tert-butoxy)disilynyl]lithium derivative in THF as shown in Scheme 4, and also a nucleophilic substitution reaction with n-butyllithium . 

SCHEME 4. Self-condensation reaction of [(tert-butoxydiphenyl)silyl]lithium (20) to give [2-(tert-butoxy)disilanyl]hthium derivative 21... 

FIGURE 21. Optimized geometries for reactive intermediate (Int), transition state (TS) and product (P) at MP2//HF/6-31G for the self-condensation reaction of Uthium(alkoxy)silylenoid. Bond lengths are in angstroms, and bond angles in degrees. Reprinted with permission from Reference 26. Copyright 1998 American Chemical Society... 

The physicochemical properties of HTs and the solid solutions produced after their calcination can be easily tuned by changing the nature and amount of metal cations and anions (10). Therefore, to elucidate the role of the chemical composition on the gas phase acetone self-condensation reaction, a series of bimetallic and trimetallic HTs were prepared, characterized and tested. 

The activity of calcined HTs was determined in self-condensation reaction of acetone (J.T. Baker) by using a fixed bed catalytic reactor with an on-line GC. Prior to the catalytic test, catalysts were pretreated in-situ under nitrogen atmosphere at 450°C for 5h. Acetone was supplied to the reactor by bubbling nitrogen gas through the acetone container at 0 °C. The reaction temperature was established at 200 C. The products were analyzed by means of GC (Varian CP-3800) using a WCOT Fused silica column, equipped with a FID detector. 

Self condensation reactions. Elaboration of a skeleton in synthesi s. 

Bisphenol-A is present as the disodium salt in the aqueous phase of the two-phase mixture. Phosgene enters the system and dissolves in the organic phase. It is believed that the reaction between phosgene and bisphenol-A occurs at the organic-aqueous interface to form the monochloroformate—Reaction 1—or bischloroformate—Reaction 2— ester of bisphenol-A. The chloroformate esters that form grow to oligomers by reaction with additional bisphenol-A or by self-condensation —Reactions 3 and 4, respectively. 

The self-condensation reaction of TEOS was predominant rather than copolymerization between PDMS and TEOS immediately after mixing. As the reaction proceeded, D decreased and D(Q) increased. Furthermore, the presence of D4C was observed. These observations indicate that bonds between PDMS and TEOS are formed in the ormosils of the PDMS/TEOS system and that the PDMS chains which contained —O—SiMe2—O— units were broken into shorter chains and/or cyclic D4C tetramers. These facts indicate that hydrolyzed TEOS reacted with —O—SiMe2—O— in the middle of PDMS chains as well with the silanol end groups, HO—SiMe2—O—, of PDMS. D and D4C remained after 10 h at 70 °C (Figure 13). The peak intensity of D after 10 h at 70 °C was about one-tenth of the peak intensity before reaction, and the peak intensity of D4C after 10 h was also... 

Generally, the preparation of symmetrical dialkylhalonium ions is simpler and the reactions are clean. Unsymmetrical dialkylhalonium ions undergo disproportionation and alkylation (self-condensation) reactions, even at low temperatures (about 30°C). 

In a similar way a ketone may undergo a self-condensation reaction to give a ketol, which may be dehydrated in a separate reaction to an a,/ -unsaturated... 

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