Condensation Reaction

A condensation reaction is a reaction between two reactants that yields one larger product and a second, smaller product such as water.

From: Principles of Organic Chemistry , 2015

Scientific Bases for the Preparation of Heterogeneous Catalysts

Moez Hasni , ... Stéphanie Delsarte , in Studies in Surface Science and Catalysis, 2006

Liquid phase aldol condensation reaction between heptanal and benzaldehyde is studied over two series of oxynitride catalysts: aluminium phosphate oxynitrides "AlPON" and mixed aluminium gallium phosphate oxynitrides "AlGaPON", with increasing nitrogen contents (0-14  wt.% for "AlPON" and 0 - 16   wt. % for "AlGaPON"). The main products are jasminaldehyde and 2-pentyl-2-nonenal. Jasminaldehyde is formed via the cross-aldol condensation reaction between heptanal and benzaldehyde and 2-pentyl-2-nonenal is formed via the self-condensation reaction of heptanal.

The nitridation of phosphate precursors (AlPO4 and Al0.5Ga0.5PO4) has a positive effect on the selectivity to cross-condensation product. Maximum selectivities are obtained over samples with intermediate nitrogen contents. Selective poisoning of the acid and the basic sites, by adding tripropylamine and benzoic acid respectively in the reactor showed that both acid and basic sites are responsible for the catalytic activity of "Al(Ga)PO(N)"catalysts.

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Sol–Gel Processing

Douglas A. Loy , in Encyclopedia of Physical Science and Technology (Third Edition), 2003

I.B Condensation Reactions

Condensation reactions involve the net formation of a siloxane bond from a silanol and an alkoxysilane, or from two silanols ( Fig. 2). The mechanisms are essentially the same as those outlined for the previously cited hydrolysis reaction. The condensation rate varies with pH with the rate increasing linearly above and below a minimum pH that varies depending upon the degree of condensation at the silicon and any organic substituents it might bear. Figure 4 shows the condensation rate plot for the first condensation reaction of an alkyltriol with the minimum at pH 4.5. The mechanism for condensation at low pH is still thought to be [S N2–Si] and at high pH (pH   >   4.5) is through the [S N2**–Si] mechanism. The minimum is between pH 1.5 and pH 2.5 for tetraalkoxysilanes because silicon becomes increasingly electrophilic as the number of electron-withdrawing siloxane bonds increases. This results in an increase in the acidity of silanols with more siloxane bonds. Monomeric silanols with no siloxane bonds have a pKa near 13   while surface silanols in silica gels have a pKa of 6. Greater numbers of siloxane bonds reduce the basicity of the oxygens in the alkoxide groups or silanols such that protonation becomes more difficult. It is no accident that the isoelectric point is at pH 2 for silica surfaces that are predominantly composed of silanols with three siloxane bonds. Below pH 2 the silanols and siloxanes can become protonated and above this pH the silanols start to become deprotonated.

FIGURE 4. Condensate rate-pH profile for an alkylsilanetriol and the average condensation rate for tetraethoxysilane (1/tgel).

Condensation under acidic conditions occurs with protonation of an oxygen atom on a silanol, alkoxide group, or siloxane followed by attack of a silanol resulting in the loss of a molecule of water or alcohol, or cleavage of a siloxane bond, respectively. Siloxane bond cleavage with loss of a silanol results in no net increase in the degree of condensation. However, this is a likely mechanism for changes in colloid structure or even aging in gels. Condensation at pH's above the rate minimum at pH 2 involves the attack of a silanolate on a silicon with the formation of a pentacoordinate intermediate and formation of the siloxane bond with loss of hydroxide or alkoxide. Again, the loss of siloxane can also occur under basic conditions and is the origin of base-catalyzed dissolution of silica.

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Advances in the Development of Biodegradable Polymeric Materials for Biomedical Applications

Rishik Patra , ... Kishor Sarkar , in Reference Module in Materials Science and Materials Engineering, 2022

Condensation

Condensation reaction suggests sequential joining of molecules by losing small molecules as byproducts. Poly-condensation is chain growth polymerization which may occur under acidic or basic condition or in the presence of catalyst producing water molecule at equilibrium. Apart from water small molecules like methanol, ammonia, acetic acid produced depending on functional groups. Peptide bonds formed during the condensation of amino acids play significant role in our daily life. Researchers found various application of condensation polymeric materials in drug delivery due to its biocompatibility. Polyoxalate derived from the reaction between oxalyl chloride and 1,4-cyclohexanedimethanol is degradable in presence of water and byproducts can be removed easily. Kim et al. (2010), Lee et al. (2009) reported that synthesized product of malic acid and 1,12-dodecanediol is applicable in bone tissue engineering as biodegradable elastomer.

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Synthetic Polymers

Robert J. Ouellette , J. David Rawn , in Principles of Organic Chemistry, 2015

15.9 Condensation Polymers

A condensation reaction is a reaction between two reactants that yields one larger product and a second, smaller product such as water. This type of reaction has been illustrated in the reactions of many functional groups containing oxygen or nitrogen. Products of condensation reactions include ethers, acetals, esters, imines, and amides.

We now consider condensation reactions that yield polymers. Two functional groups are required in a monomer so that after one functional group reacts, the other is available to link to another monomer. The functional groups in monomers may be arranged in two ways for condensation polymerization.

A single compound can contain two different functional groups such as an amino group and a carboxylic acid group. Reaction of the amino group of one molecule with the carboxylic acid of another molecule gives an amide that still has a free amino group and a free carboxylic acid group, which can continue to react to form a polymer. The general reaction is shown below.

Continued reaction of the carboxylic acid end with the amino group of another monomer or of the amino group end with the carboxylic acid group of another monomer yields a homopolymer.

Condensation reactions also result from the copolymerization of two monomers. Each monomer contains two of the same functional group. Examples include the reaction of a monomer that is a dicarboxylic acid with a monomer that is a diol. The functional groups on one monomer can only react with the functional groups on the other monomer. The general reaction is shown below.

Continued reaction of the carboxylic acid end with the hydroxyl group of the diol monomer or of the hydroxyl group end with the carboxylic acid group of the dicarboxylic acid monomer yields a copolymer.

A monomer can contain two different functional groups, but such monomers are not widely used. First, these monomers are more difficult to prepare without uncontrolled polymerization during their synthesis. Second, the monomer can only be used in one possible polymerization reaction. Condensation polymers formed from two different monomers are more common. The synthesis of each monomer is usually straightforward and less expensive. Each monomer can be used in reactions with other monomers. For example, any of a series of dicarboxylic acids can react with any of another series of diols.

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Synthesis and processing of hydrogels for medical applications

F. Redaelli , ... F. Rossi , in Bioresorbable Polymers for Biomedical Applications, 2017

10.8.2 Polycondensation

Condensation reactions between hydroxyl groups or amines with carboxylic acids or derivatives are frequently applied to the synthesis of polymers to yield polyesters and polyamides, respectively. These reactions can also be used for the preparation of hydrogels ( Tomida et al., 1997; Santoro et al., 2011).

For example, Rossi and coworkers (Rossi et al., 2015b; Sacchetti et al., 2014) studied the polycondensation reaction between high-molecular-weight branched polyacrylic acid (carbomer 974P) and agarose through microwave-assisted chemistry. The solvent used was phosphate-buffered solution and its role in hydrogel chemistry was already described. In brief, because carbomer 974P is highly pH sensitive, the buffered nature of the solvent allowed for the possibility to control and tune the reaction. Before polymeric solution irradiation, polymer chains are not overlapped and segmental mobility is high. With increasing irradiation doses, intramolecular links and chain scissions are favored. This leads to the decrease of segmental mobility and allows intermolecular cross-links to be formed and thus give origin to local three-dimensional networks, also known as "microgels." Further irradiation increases privileged intermolecular cross-linking and chain scission, giving rise to macroscopic gels. In general, chemical interactions would statistically bring polymer chains together and, indeed, the formation of a stable structure occurs through junction zones between chains.

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A critical review of the 1999 literature preceded by three chapters on current heterocyclic topics

Robert D. Larsen , Jean-Francois Marcoux , in Progress in Heterocyclic Chemistry, 2000

6.1.5 ACRIDINES

Condensation reactions are a common approach to the synthesis of acridines. The Bemthsen reaction can be applied to the synthesis of 9-acridinylalkanoic acids. Diphenylamine is condensed with dicarboxylic acids in the presence of ZnCl 2 to afford a mixture of the bis-acridinyl alkanes and acridinylalkanoic acids depending on the stoichiometry <99SC4007>. The Friedlander reaction under Fehnel conditions <99TL4097> and Ullmann condensation/Friedel-Crafts acylation <991SL641, 99S947> are commonly used to prepare the acridine and acridinone rings, respectively. Nafion-H is a useful acid catalyst for the intramolecular Friedel-Crafts acylation of N-(2'-carboxyphenyl)aniline to afford the acridinone <99SL1067>. Amination of benzyne with the o-aminobenzoate 55 followed by Friedel-Crafts acylation provides the acridinone <99TL7003>. A diimine was reported to add to benzyne in a [2+2] fashion forming a benzazetidine followed by electrocyclization and aromatization to produce the acridine ring system <99T1111>.

Photocyclization of the condensed adduct 56 between 2-methyl-4-oxoquinoline and cinnamaldehyde gives the acridine 57 <99ZN(B)1337>. This approach is notable for its application to the synthesis of the hitherto unknown 1-phenyl and 1-naphthacridones.

Substitution of the nine position is a common transformation for acridines. An optimized method for preparing the 9-carboxamides uses BOP/DMF <99SC4341>. Reaction of 9-isothioacridines with the sodium anion of diethylmalonate is followed by alkylation with bromoacetate to afford the spiro[dihydroacridine-9(10H)-thiazolidines] <99H(51)137>.

N-Methyl-9-t-butylacridine undergoes oxidation to acridine with loss of the methyl and t-butyl groups by treatment with PhIO <99TL5425>. Acridine can be converted to the diols and tetraols under biocatalysis conditions <99CC1201>.

Acridine-4,5-diol was converted to the corresponding 18-crown-6 ligand by alkylation of the hydroxy groups with tetraethylene glycol di-p-tosylate <99T1491>.

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Gelation

C. Jeffrey Brinker , George W. Scherer , in Sol-Gel Science, 1990

6 SUMMARY

Condensation reactions produce polymeric clusters whose growth kinetics and fractal structure follow the predictions of kinetic models based on Smoluchowski's equation. As the clusters grow, their density decreases (because d f < 3), so the effective volume fraction of polymer increases. Eventually the clusters overlap and become nearly immobile, so that further bonding involves a percolative process with the "sites" being filled by large (∼micron) polymeric clusters. The evolution of the properties in the vicinity of the gel point is generally in agreement with the critical behavior predicted by percolation theory, and in contradiction to the classical theory. This is particularly true when the critical behavior is established using pairs of properties (as in Eq. 51), presumably because these are the most reliable experiments. Much less consistent (or trustworthy) results have been found in direct measurements of the divergence as a function of the departure from the critical point (t − t gel).

The reactions that bring about gelation continue long after the gel point. In the next chapter we examine the long-term aging of gels, during which they may stiffen, coarsen, and shrink.

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Organic film formers

J. Bentley , in Paint and Surface Coatings (Second Edition), 1999

2.10.2 Formulating

The condensation reactions involved, particularly the main formaldehyde addition and etherification reactions, are reversible, and so excess formaldehyde and alcohol concentrations are necessary to push equilibria towards the desired products. When formulating resins the ratio of formaldehyde to melamine or urea determines the degree of methylolation. With urea charging 2.4 mol of formaldehyde to attain the normally required 2 mol addition may be necessary; with melamine resins, where reactivities up to 6 are both possible and useful, a wide range of ratios may be used. The quantity of alcohol included, along with the processing conditions, then determines the degree of alkylation and polymerization, and the characteristics of the final resin. Again, a considerable excess of alcohol is normally required to be present, though its presence in the final resin helps storage stability. Reactivity of butylated melamine resins, for example, increases with decreasing formaldehyde to melamine ratio, and with decreasing degree of etherification.

Unlike other resins, specifying with accuracy the ratio of reactants actually incorporated into the resin is not possible; rather, specifying the ratio of reactants charged initially may be more meaningful.

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Functional Classes II, Reactions

Gregory Roos , Cathryn Roos , in Organic Chemistry Concepts, 2015

7.7.2 Condensation Reactions with 1° Amino Derivatives

A condensation reaction is made up of an addition and elimination reaction sequence. As Figure 7.32 shows, ammonia and 1° amine derivatives can be used in these reactions. Table 7.4 lists some condensation examples with aldehydes and ketones to give products in which the nitrogen replaces the carbonyl oxygen.

FIGURE 7.32. Primary amino-carbonyl condensation reaction.

Table 7.4. Amino-Carbonyl Condensation Products

Amino Reagent Product Class
Amine
Imine
Hydroxylamine
Oxime
Hydrazine
Hydrazone

These products are usually crystalline solids with sharp melting points. This feature means these derivative products can be used as standards to identify many common aldehydes and ketones.

The best known example is the 2,4-dinitrophenylhydrazone derivative, or 2,4-DNP. Figure 7.33 shows how these are made by reaction of carbonyl compounds with Brady's hydrazine reagent to give the orange-red colored derivatives. The appearance of the 2,4-DNP precipitate is a visual test for aldehydes and ketones.

FIGURE 7.33. Brady's test for aldehydes and ketones.

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Five-membered Rings with More than Two Heteroatoms and Fused Carbocyclic Derivatives

David J. Wilkins , Paul A. Bradley , in Comprehensive Heterocyclic Chemistry II, 1996

4.08.9.7 Type F Syntheses

The condensation reaction of cyclic amidines with trichloromethylsulfenyl chloride yields sulfenamides, which afford 5-arylimino-1,2,4-thiadiazolines on treatment with aromatic amines 〈84CHEC-I(6)463〉. An example of this type of reaction starting from 2-amino-4-arylthiazoles ( 271 ) affords 3H-thiazolo[2,3-c]-1,2,4-thiadiazoles ( 272 ), via the sulfenamide ( 270 ) (Scheme 60) 〈88IJC(B)501〉.

Scheme 60.

1,2,4-Thiadiazole S,S-dioxides ( 274 ) have been prepared by the cyclization of N-halomethylsulfonyl amidines and guanidines ( 273 ) (Equation (41)) 〈84CHEC-I(6)463〉.

(41)

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