Appearance Paraformaldehyde

Zavitsas et al. added terms for the extent of hemiformal and paraformaldehyde formation. Hemiformal formation slows the methylolation reaction as does the presence of paraformaldehyde. They report that only monomeric methylene glycol appears to methylolate. They point out that the terms for the two polyoxy-methylene species partially cancel one another, as depolymerization of paraformaldehyde naturally occurs while hemiformal formation is increasing due to methylolation. They observe that hemiformals form only on the methylolphenol hydroxyls and not on the aromatic hydroxyl. They calculate that the average number of methoxy groups involved in each of the hemiformals is about two in addition to the original methylol. There is no selectivity for ortho versus para positions in hemiformal formation. 

Another way to disconnect a terminal epoxide is to add a functionalized ylide to paraformaldehyde. This was the route explored by Solladie-Cavallo, who treated two aromatic ylides with paraformaldehyde at low temperatures and obtained good selectivities (Scheme 1.14) [22]. It would thus appear that this is the best ylide-mediated route to terminal aromatic epoxides to date. 

Chloromethyl esters are obtained quite readily by the action of paraformaldehyde on the appropriate acid chloride in the presence of a small quantity of zinc chloride as catalyst.1 It therefore seemed worth while to try the action of paraformaldehyde on fluoroacetyl fluoride, but the only product which could be isolated was a low-melting solid which appeared from its reactions to be methylene bisfluoroacetate, CH2(0 CO CH2F)2. The compound was submitted for physiological tests, and it was shown that the l.d. 50 subcutaneous injection into mice was about 10 mg./kg. Subcutaneous injection into rats with doses of 2-5, 5 and 10 mg./kg. all killed 1/1. 

The direct formation of tetrazocane tetracarbamates has been reported to occur in fairly good yields by refluxing methylenebis(carbamates) (333) with paraformaldehyde in the presence of toluenesulfonic acid. Under these conditions the tetrazocanes (335) appear to... 

In a 5-L, three-necked, round-bottomed flask fitted with a 30-ml. dropping funnel, mechanical stirrer, and thermometer extending down into the liquid is placed a suspension of paraformaldehyde (trioxymethylene, 125 g., 4.16 moles) in freshly distilled (Note 1) nitromethane (2.5 1., 46.6 moles). The suspension is stirred vigorously, and 3N methanolic potassium hydroxide solution is added dropwise from the dropping funnel until, at an apparent pH of 6-8, but closer to pH 8 (pH paper), the paraformaldehyde begins to dissolve and the suspension assumes a clearer appearance. About 10 ml. of the alkaline solution is required, and the addition takes about 10 minutes. About 15-20 minutes after addition of the alkaline solution is complete, the paraformaldehyde dissolves completely. Shortly thereafter, the solution temperature reaches a maximum of 13-14 degrees above room temperature and then slowly drops. Stirring is continued 1 hour after addition of the alkaline solution is complete. 

This observation also appears to explain why an excess of paraformaldehyde should have a harmful influence on the yield of cyclonite. In particular, Winkler noticed that the addition of formaldehyde to a hexamine solution in aqueous acetic acid causes the decomposition of hexamine which proceeds at a rate depending on the ratio of formaldehyde to hexamine. 

Dioxacyclohexanes can be produced in excellent yields from aliphatic or aryl-substituted alkenes.64 Dilute sulfuric acid at or above room temperature with paraformaldehyde appears to give the best results. Dioxane-water or acetic acid as solvent was found to afford increased yields in the Prins reaction of arylalkenes. 

Fig. 1 (appears on p. 63). Distribution of FITC-conjugated BSA in various fibroblast cell lines under different fixation/permeabilization regimes. (A-D) Protein distribution in living cells—PtKi, CHO, 3T3, and HeLa cells, respectively. The protein is excluded from the nuclei of all cells. (E-H) Protein distribution in cells extracted for 10 min with 0.1% Triton X-100 before fixation for 30 mm with 3.7% formaldehyde—PtKi, CHO, 3T3, and HeLa cells, respectively. Nuclear fluorescence is seen in PtK) (E) and 3T3 (G) cells. (I-L) Protein distribution in cells extracted for 10 mm with 1% Triton X-100 before fixation for 30 min with 3.7% formaldehyde—PtKj, CHO, 3T3, and HeLa cells, respectively. No fluorescence is detected m the cells with the exception of some nuclear fluorescence seen m HeLa cells (L). (M-P) Protein distribution in cells fixed for 30 min with 3.7% paraformaldehyde before permeabilization for 10 min with 0.1% Triton X-KK). Fluorescence is seen primarily in the cytoplasm with the exception that nuclear fluorescence is seen in PtKi (M) and CHO (N) cells. (Q-T) Protein distributions in cells fixed for 5 min with 90% methanol, 50 mM EGTA at -20°C—PtKi, CHO, 3T3, and HeLa cells, respectively. All cells show an overall low fluorescence, fibrous-textured cytoplasmic fluorescence and bright staining at the periphery of the nucleus, 10 pm per scale division (black bar). Reproduced with permission from ref. 6. 

The hydrate of formaldehyde, HOCH2OH, may under certain conditions polymerise in aqueous solution to form paraformaldehyde, H0CH2(0CH2) 0CH20H, which appears as a white deposit in the solution. The polymerisation may be prevented by adding to the solution 10-15% of methanol. 

In this experiment it is shown that a CH2OH group can be successfully introduced by reaction of the organolithium compound with (dry) paraformaldehyde [3]. For obtaining good yields of the corresponding alcohol, it appeared to be necessary to use a large excess (at least 400 mol%) of the polymeric aldehyde. 

A report has also appeared on the alkylation of aldehydes and ketones by polyfluoroalkoxyphosphoranes (62), which in the cases of paraformaldehyde, aromatic or unsaturated aldehydes, and hexafluoroacetone gives polyfluoro-alkyl-containing acetals [e.g., (63)]. 

Formaldehyde also appears on the market as the hydrated solid polymer paraformaldehyde, containing about 95 per cent formaldehyde, which is prepared by the evaporation of formaldehyde solution. 

Steroidal and other primary amines were converted into perhydro-dioxazepines, for example (58), by treatment with paraformaldehyde and a i)/c-diol. °° Deamination of N,N-dimethylamines with CCI3CH2OCOCI was exemplified by the conversion of the 3a-dimethylaminopregnane (59) into the A -compound. The deamination appears to be controlled by stereoelectronic factors as conessine underwent demethylation to give (60). Cleavages of 16a,17a-epimino-20-oxo-steroids and their 20-hydrazones with thioacetic acid were reported, as were the reactions of 16a,17a-episulphides with HSCN... 

Section 3.1. outlines several protocols for fixation using as an example the fixative paraformaldehyde, and the recipes for the relevant solutions are given. Numerous other fixatives are available—and others indeed may be preferable— depending on the tissue and the characteristics of the antigen. A list of several alternative fixatives and recipes appears in Section 2.S. and appropriate notes relating to their use are provided although use of these alternative fixatives is not explicitly detailed in the protocols. 

The specificity of the NADPH diaphorase staining technique for NOS is dependent on aldehyde fixation. For unknown reasons, the NADPH diaphorase activity of NOS is resistant to fixation, whereas the NADPH diaphorase activity of other NADPH-requiring enzymes in the brain is destroyed by aldehydes (14). Fixation in 4% paraformaldehyde for 4 h at 4°C should provide sufficient fixation for small pieces of tissue (<0.5 cm ). Longer fixation times or fixation at room temperature should be used if the staining observed appears nonspecific (i e., if all of the tissue stains purple)... 

Phase-contrast microscopy provides a fast and reliable way to evaluate the onset of sperm chromatin decondensation and the appearance of nuclei assembled in vitro (Fig. 1). After incubation, a IO-/1I aliquot of the incubation mixture should be taken and immediately fixed with an equal volume of 8% (w/v) paraformaldehyde in 154 mM PIPES-NaOH, pH 7.5, for 5 min on ice. After fixation, samples should be diluted with an equal volume of extraction buffer as specified above. Then, 5-ix aliquots of this mixture may then be mounted for viewing between slide and cover slip. To ensure adequate separation between the slide and cover slip, about 2 /xl of melted bee s wax should be deposited onto each corner of the cover slip before mounting. 

Acetal, (Polyacetal) Poly-oxymethylene (POM) Acetal is a polymer obtained through an addition reaction of formaldehyde — (CH2—0) . It excels in mechanical performance and is regarded as a prominent engineering polymer. It appeared in 1959 with the commercial name Delrin . A short time later a useful copolymer was also developed with a cyclic ether like ethylene oxide. The monomer formaldehyde is a gas produced mostly by oxidizing methanol, and it is very useful in thermoset polymers like phenol, urea and melamine-formaldehydes. For high purity it is initially converted to trioxane or paraformaldehyde. The polymerization is carried out by ionic mechanism, wherein the monomer is dispersed in an inert liquid (heptane). The molecular weights reach 20,000 to 110,000. 

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