Formaldehyde in acid

Morphine (1) reacts with formaldehyde in acidic solution to yield a cyclic ketoalcohol (2) which is transformed into the colored oxonium (3) or carbenium ion (4) in acidic conditions [10],... 

All acid-catalyzed electrophilic substitution reactions are held by Treibs to occur by way of the distinct reactive species (23), thus the very greatly accelerated interaction of pyrrole and formaldehyde in acid solution involves attack of neutral formaldehyde on (23). Another example is the interaction of 2,3,4,6-tetramethylpyrrole with p-dimethylaminobenzaldehyde in acid solution, for which the following reaction (Scheme 2) is given,(23a) being presumably intended... 

The ene reaction is strongly catalyzed by Lewis acids such as aluminum chloride and diethylaluminum chloride204 Coordination by the aluminum at the carbonyl group increases the electrophihcity of the conjugated system and allows reaction to occur below room temperature, as illustrated in Entry 6. Intramolecular ene reactions can be carried out under either thermal (Entry 3) or catalyzed (Entry 7) conditions 205 Formaldehyde in acidic solution can form allylic alcohols, as in entry 1. Other carbonyl ene reactions are carried out with Lewis acid catalysts. Aromatic aldehydes and acrolein undergo the ene reaction with activated alkenes such as enol ethers in the presence of Yb(fod)3 206 Sc(03SCF3)3 has also been used to catalyze ene reactions.207... 

Aminoacridine derivatives reacted with formaldehyde in acidic medium to form (depending on the stoichiometry) various condensation products, among them 3,4-dihydro-l//-l,3-oxazino[4,5-f]acridines <1997X2891, 1998H(48)755, 2001J(P1)2962, 2006BML4641>. 

Poly(thioformaldehyde) can also be obtained by reaction of hydrogen sulfide with formaldehyde in acid media (8). Again the key intermediate is 1-hydroxy-2-oxa-4,6-dithioheptane-7-thiol. Though acid conditions favor formation of trithiane, use of a high CH20/H2S04 ratio results only in polymer formation. Credali and Russo (8) believe this to be a topochemical reaction between the dithioheptane and mercaptomethanol. 

In the above paragraph it was shown that the lignin Cg units can be polymerized at the 2- and 6-positions with formaldehyde in acidic aqueous dioxane. The polymerization reaction proceeds presumably via a hydrox-ymethylated intermediate which was isolated in low yields only when large excesses of formaldehyde were employed. If the hydroxymethylation of the meta position can be achieved in high yield it would clearly afford a very... 

Table I. The reaction of 4-hydroxy-3,5-dimethoxyphenyl ethane (13) with formaldehyde in acidic aqueous dioxane at 80°C (14)...

Novolacs are obtained by the reaction of phenol and formaldehyde in acidic conditions. Novolac oligomers are linear or slightly branched addition products linked by methylene bridges (molar masses in the range 500 5000 g mol-1). The reaction is usually carried out using a molar ratio CH20/ PhOH close to 0.8, to avoid gelation in the reactor (see Chapter 3) ... 

The reaction of alkyl- and aryldichlorophosphines (or phos-phonous acids) with N-benzylglycine and formaldehyde in acidic solution yields (N-benzyl-N-hydroxycarbonylmethyl-aminomethyl) alkyl- and -arylphosphinic acids of structure 1 (R = alkyl, HOCH2) " " " depending on the electronegativity... 

The first synthetic polymers to be of any use were the phenol formaldehyde resins of which the most famous, Bakelite, was discovered by Bakeland at the turn of the century. He combined phenol and formaldehyde in acid solution and got a reaction that starts like the bisphenol A synthesis. 

The condensation of resorcinol, chloroacetic add, and formaldehyde in alkaline medium gives a bifunctional cation-exchange resin containing COOH and —OH groups95. The condensation of salicylic add with formaldehyde in acid medium followed by treatment with phenol in alkaline medium also gives a bifunctional resin which is suitable for separation and purification of proteins 96). A bifunctional cation-... 

Formation of condensation structures is the reason for gelation of solutions of various natural and synthetic polymers. Gelation may be accompanied by conformational changes of macromolecules, which occur in the case of gelling of gelatin and other biopolymers, or in the course of chemical reactions. For instance, according to Vlodavets, partial acetalization of polyvinyl alcohol with formaldehyde in acidic medium under the conditions of supersaturation yields fibers of polyvinyl formals which further undergo coalescence and form a network with properties similar to those of leather (and artificial leather substitute). 

The reaction of 3-aminoacridines with formaldehyde in acidic medium has been studied <97T2891>. The products vary depending on the stoichiometry of the formaldehyde. With trifluoroacetic acid as the acid the acridine analogue of Troger s base is prepared <97BSF495>. 

Verdazylium salts 13 can be obtained in high yield by reacting the corresponding triphenylformazans with formaldehyde in acid media in a two phase system (CHCV HjO). The reduction of the salts with ascorbic acid in the two phase system gives the verdazyl radicals, whereas in methanol leucoverdazyls are obtained <97S 17>. 

CMC can be crosslinked with epichlorhydrine (in alkaline conditions) or formaldehyde (in acidic conditions) to give cation-exchange gels or ultrafiltration membranes [34, 35]. At low pH, CMC may form crosslinks through lactonization between carboxylic acid and free hydroxyl groups. 

The epoxy novolac resin was prepared by two step reactions. The first step was involved in the formation of novolac resin through chemical reaction between phenol and formaldehyde in acid environment. In the second step, the epoxidation of previously prepared novolac resin was carried out by reacting epichlorohydrin with a novolac resin in a specific molar ratio. The detail of the synthesis of novolac resin and its epoxidation was described in our previous report [19,20]. The typical properties of the synthesized ENR are given in Table 16.2. 

The anodic oxidation of formaldehyde in acid media yields CO2 at essentially 100% current efficiency. From controlled potential oxidation experiments, it was reported that the amount of formaldehyde which is oxidized is independent of the anode potential between 0.4 and 1.0 V (N.H.E.). In basic solutions the main reaction product is formate which is only slowly oxidized in alkaline media. ... 

The antimicrobial efficacy of the amine-formaldehyde reaction products essentially corresponds to the formaldehyde content of these compounds. Known exceptions are HTA, hexahydro-oxadiazines and octahydro-s-tetrazines, which derive from ammonia respectively certain alkylolhydrazines (Paulus, 1980) here the detection of formaldehyde by the Taimenbaum methods gives a negative result, which means that these substances have no significant antimicrobial effect at neutral to alkaline pH they release formaldehyde in acidic media only. This pH dependency is broken off, if, for example, HTA is quatemized (Jacobs et al., 1916). In contrast to HTA the quaternary hexaminium salts release formaldehyde widely independent of pH and therefore may be used as preservatives also for media of neutral to alkaline pH. They are not comparable with the surface active conventional quaternary ammonium compounds (QACs see Section 16.1)... 

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