Paraformaldehyd

The Mannich Reaction involves the condensation of formaldehyde with ammonia or a primary or secondary amine and with a third compound containing a reactive methylene group these compounds are most frequently those in which the methylene group is activated by a neighbouring keto group. Thus when acetophenone is boiled in ethanolic solution with paraformaldehyde and dimethylamine hydrochloride, condensation occurs readily with the formation of... 

Add 5 ml. (5 g.) of acetophenone, 1-25 g. of finely powdered paraformaldehyde, and 3 5 g. of dry dimethylamine hydrochloride to 8 ml. of absolute ethanol, and then boil the mixture under reflux for 1-5 hours. Filter the solution (which is now almost entirely clear) through a preheated filter-funnel, and cool the filtrate in ice-water with stirring. The propiophenone hydrochloride rapidly separates as white crystals filter oflF the crystals at the pump and recrystallise from a small quantity of ethanol m.p. 155-156°. Yield, 2 5 g. 

It is marketed as a 35-40 per cent, solution in water (formalin). The rpactions of formaldehyde are partly typical of aldehydes and partly peculiar to itself. By evaporating an aqueous solution paraformaldehyde or paraform (CHjO), an amorphous white solid is produced it is insoluble in most solvents. When formaldehyde is distilled from a 60 per cent, solution containing 2 per cent, of sulphuric acid, it pol5unerises to a crystalline trimeride, trioxane, which can be extracted with methylene chloride this is crystalline (m.p. 62°, b.p. 115°), readily soluble in water, alcohol and ether, and devoid of aldehydic properties ... 

When ammonium chloride is heated to a higher temperature (160°) with a large excess of anhydrous formaldehyde (as paraformaldehyde), trimethyl-amine hydrochloride (trimethylammonium chloride) may be obtained ... 

Mix 100 g. of ammonium chloride and 266 g. of paraformaldehyde in a 1-litre rovmd-bottomed flask fitted with a long reflux condenser containing a wide inner tube (ca. 2 cm. diameter) the last-named is to avoid clogging the condenser by paraformaldehyde which may sublime. Immerse the flask in an oil bath and gradually raise the temperature. The mixture at the bottom of the flask liquefies between 85° and 105° and a vigorous evolution of carbon dioxide commences at once remove the burner beneath the oil bath and if the reaction becomes too violent remove... 

The formaldehyde may be replaced by methylal CHjlOCH,), or by chloro-methyl ether CHjOCHjCl, produced from paraformaldehyde, hydrogen chloride and methyl alcohol ... 

Into a 1-litre three-necked flask, equipped with a reflux (double surface) condenser, a mechanical stirrer (preferably of the Hershberg type. Fig. II, 7, 8) and a gas lead-in tube extending to near the bottom of the flask, place 200 g. (227 ml.) of dry benzene, 20 g. of paraformaldehyde (1) and 20 g. of finely-pulverised, anhydrous zinc chloride. Support the flask on a water bath so arranged that the level of the water in it is about... 

We chose benzyli dene acetone (4.39, Scheme 4.11) as a model dienophile for our studies. The uncatalysed Diels-Alder reaction of this compound with cyclopentadiene is slow, justifying a catalytic approach. Reaction of 4.39 with paraformaldehyde and dimethyl amine under acidic conditions in an aqueous ethanol solution, following a literature procedure, produced the HCl salt of 4.42 (Scheme 4.11). The dienophile was liberated in situ by adding one equivalent of base. 

Finally, in the last step, the chelating auxiliary had to be removed Ideally, one would like to convert 4.54 into ketone 4.55 via a retro Mannich reaction. Unfortunately, repeated attempts to accomplish this failed. These attempts included refluxing in aqueous ethanol under acidic and basic conditions and refluxing in a 1 1 acetone - water mixture in the presence of excess paraformaldehyde under acidic conditions, in order to trap any liberated diamine. Tliese procedures were repeated under neutral conditions in the presence of copper(II)nitrate, but without success. 

Fortunately, under moderately acidic conditions, in the presence of acetone and paraformaldehyde, 4.54 undergoes an elimination reaction similar to that described in Scheme 4.13, producing oc,(3-... 

This is the least desirable of all three processes [What do you mean by that This is really easy to do And the yield are fine ]. The yields are lower than the two rearrangements, and it requires substantial labor to get a decently pure product. Not "labor" as In difficult but "labor" as in a lot of it. I would suggest this only for those who have a large supply of Formaldehyde available to them (note - N. Coffey found formaldehyde at Home Depot - look for "Mildewcide" and dissolve it in enough water to make a 37% solution to depolymerize the paraformaldehyde). 

Hexamine, more formally known as Hexamethylenetetramine, is easily and conveniently produced from Formaldehyde and Ammonia solutions. Formaldehyde may be easily produced by depolym-erizing, with heat, Paraformaldehyde (the only ingredient in OTC MildewCide). Hexamine is then reacted with Hydrochloric Acid and heated to yield Methylamine HCI in near quantitative yield. 

Place 3 3oz packets of Mildewcide into a 1L flask with an electric heating mantle and cork in the neck connected to a gas bubbler immersed in at least 550mL of distilled water. Heat the paraformaldehyde (what is in the Mildewcide) to between 180-200C (a temp, regulator is absolutely necessary for this step or use a silicone oil bath). The paraformaldehyde will depolymerize making formaldehyde gas in about 91% yield. Alternatively, the gas can be bubbled through the Ammonia solution directly (only for the brave ). If the Formaldehyde solution will not be used immedi-... 

Note 2. Prepared by introducing gaseous HCl at -10°C into a mixture of 30 g of paraformaldehyde (corresponding to 1 mol of formaldehyde) and 1 mol of ethanol, until copious fumes escaped from the mixture. This was cooled (without stirring) to -70°C and the upper layer was decanted from the solid (frozen hydrochloric acid) and mixed with 50 g of yy-diethyl(or dimethyl)aniline. Subsequent distillation in a partial water-pump vacuum afforded the desired chloroether (b.p. about 40°C/40-50 mmHg). 

In the flask were placed 60 g of powdered paraformaldehyde, 100 ml of dioxane and 3 g of copper(II) acetate and 0.3 mol of liquid dimethylamine was added at -20 C. The temperature was allowed to rise gradually to 40-45°C with occasional cooling and when the reaction had subsided, the mixture was cooled to 20°C and a second portion of 0.3 mol of the amine was added. When this had reacted, the remainder of the 2.0 mol of dimethylamine was added in the same way. The mixture... 

These amines are also synthesized by refluxing 2-aminothiazole with paraformaldehyde and acetophenone in ethanol (Scheme 6) (39) or by alkaline alkylation of 2-acetamidothiazole followed by hydrolysis (40-44). 

The synthesis of 9H-benzo[2,l-e]thiazolo-[2,3-c]-as-triazine (401) was achieved by oxydative cyclization of 2-imino-3-(o-aminophenyl)-4-phenyl-4-thiazoline (718, 719). This latter reacts also with paraformaldehyde in hot toluene yielding 3-phenyl-9H.10H-benzo[l,2-/]thiazolo-[2,3-d][l,3,5]triazepine (402) (720). This heterocyclic sytem is also formed when carboxylic acids replace paraformaldehyde (Scheme 230) (721). 

Butynediol. Butynediol, 2-butyne-l,4-diol, [110-65-6] was first synthesized in 1906 by reaction of acetylene bis(magnesium bromide) with paraformaldehyde (43). It is available commercially as a crystalline soHd or a 35% aqueous solution manufactured by ethynylation of formaldehyde. Physical properties are Hsted in Table 2. 

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