Méthanal

Properties

Although the méthanal is a gas with room temperature, it is very water soluble, in which it forms a solution of formol . The méthanal polymerizes in water, with the result that the formol contains few méthanal in the form of Monomère S of H₂CO formula. Generally, the formol sold in the trade contains also Méthanol to limit the polymerization of the méthanal.

The méthanal has the majority of the chemical properties of the Aldéhyde S, put aside the fact that it is more reactive. Moreover, it is remarkably électrophile, and can react by aromatic Substitution électrophile with the aromatic compounds or by Addition électrophile on the Alcène S. In the presence of a basic Catalyseur, the méthanal undergoes a Réaction of Cannizzaro and transforms into Acid formic and Méthanol.

Lastly, the méthanal is easily oxidized by the Dioxygène of the air to form formic Acid . This is why it is necessary to preserve the méthanal in quite tight containers.

Production

The méthanal is produced industrially by the catalytic Oxydation of methanol. The catalysts most employed are the metal money, or a mixture of oxide of Fer, Molybdène and Vanadium. In this case, methanol and the dioxygene react to 400 °C according to the equation:

CH₃OH + ½ O₂ → H₂CO + H₂O

The catalysis containing money reacts to higher temperatures, about 650 °C. Two reactions then produce simultaneously méthanal: the equation above, and the equation of Dehydrogenation below.

CH₃OH → H₂CO + H₂

The prolonged oxidation of the méthanal leads to the formic formation of Acid, that one finds in weak concentration in the industrial solutions of méthanal. On a reduced scale, the formol can be produced thanks to various reactions like the conversion of the ethanol.

Use

The méthanal kills the majority of the bacteria, this is why one uses formol like Disinfecting, in particular in veterinary medicine (foot baths of disinfection), or to preserve corpses of animals or the human ones. It is also used like preserving in the Vaccin S. In medicine, one employs it locally to drain the Peau, as in the treatment of the Verrue S. the solutions of méthanal are also employed for embaumer the bodies on standby of a Enterrement.

More the important quantity of méthanal is however employed for the production of Polymère S and chemicals. Compound with the phenol, the Urea or the Melamine, the méthanal form a resin thermodurcissante. These resins are often used in the permanent Colle S, like those used in the manufacture of agglomerate, Contreplaqué or Tapis, or to form synthetic foams. The production of resins containing méthanal represents more half of consumption of this one.

One employs the méthanal to produce many other chemicals, whose majority are Polyol S like the Pentaerythritol, used in the manufacture of Peinture S and of Explosif S. One counts also others derived from the méthanal like the methylene diphenyl diisocyanate, an important component of paintings and foams of Polyuréthane, as well as the hexamethylene tétramine, used in the resins phenol-méthanal and to manufacture RDX (an explosive).

The formol is also used in Biologie for the conservation of samples or taking away within the framework of analyzes IBGN, IBMR or IOBS.

In dentistry, the formol is built-in direct form (formaldehyde) or derived (paraformaldehyde, polyoxymethylene) in a great number of specialities intended to seal the channels of the devitalized teeth. Contrary to the drugs, the products and materials employed in dentistry are not subjected to a marketing authorization, which explains why they escape the regulation below.

In the field of the regulation of the phytopharmacological products, under the name of formaldehyde:

for the European Union: this active substance is prohibited by the decision 2007/442/CE following the examination relating to the inscription with appendix I of the Directive 91/414/CEE.
for the France: this active substance is not authorized in the composition of preparations profiting from a marketing authorization. The products containing of formaldehyde have a time with the distribution fixed at June 30th, 2008, and a time with the use fixed at December 20th, 2008, by the opinion published with the Official journal of October 31st, 2007.

Health

In June 2004, the formaldehyde was classified like “Cancérigène some” by the international Center of research on the cancer (CIRC), which depends on the the World Health Organization (WHO). Hitherto, he was regarded only as “probable carcinogen”. He is at the origin of cancers of the oral cavity, the nasal fossae, the sine, and its implication in the Leucémie S is considered to be quasi certain.

The méthanal is employed in many synthetic materials; however those slacken during the time of the considerable quantities of méthanal. This is why the méthanal is one of the most widespread Polluant S inside the dwellings. Above a concentration of 0,1 mg/kg in the air, it can irritate the eyes and the mucous membranes, causing Conjonctivite S, headaches and difficulties of breathing accompanied by pains in the throat.

Important exposures to the méthanal, as the absorption of formol are mortals. The méthanal transforms into Acid formic in the body, thus increasing acidity Sang uine, causing a Respiration jerked, Hypothermie, then the Coma, even the Mort. In the event of ingestion of méthanal, it is necessary to go to consult at once.

The animals of laboratory subjected to important amounts of méthanal during their life see the risk of Cancer Nez and throat to increase. However, certain studies suggest that the concentrations of méthanal in the buildings do not have an effect Carcinogène. The méthanal is classified like carcinogenic some.

In dentistry, the small quantities incorporated in the canal pastes can nevertheless cause allergic reactions. Cases of urticaria and strong allergic reactions energy to the edema of Quincke, occurring in the hours following the introduction of the paste into the dental channels, are reported in the literature.

Sentences of risk and councils of prudence

R: 23/24/25 (Poison by inhalation, contact with the skin and ingestion)
R: 34 (Causes burns)
R: 40 (suspecté cancerogenic Effect: insufficient evidence)
R: 43 (Can involve a sensitizing by contact with the skin)
S: 1/2 (To preserve under key and out of reach children)
S: 26 (In the event of contact with the eyes, to immediately wash to consult an ophthalmologist)
S: 36/37/39 (To wear protective clothing adapted, gloves and an apparatus of protection of the yeux/du face)
S: 45 (In the event of accident or Malayan to consult a doctor immediately and to show him packing or the label)
S: 51 (To use only in well broken down zones)

Health at the work

The formaldehyde is mainly used in the production of adhesives which use the manufacture of agglomerated panels, plywood, pieces of furniture and other products of wood. One also employs the formaldehyde in the manufacture of various plastics, certain fertilizers, resins used in the moulds of sand foundry, as well as certain paintings and varnish. The industry of the textile calls upon these resins like finishes to return the fabrics infroissables. It is also used for the synthesis of other chemicals. Lastly, one has recourse to formaldehyde for his bactericidal properties in many formulations of disinfectants, cosmetics, liquids of embalming and solutions of biological fabric conservation.

The professional exposure to formaldehyde by inhalation comes mainly from three types of sources: thermal decomposition or chemical of the resins containing formaldehyde, the formaldehyde emission ascribable to the aqueous solutions (for example, liquids of embalming), or formation of formaldehyde resulting from the combustion of a variety of organic compounds (for example, exhaust fumes). In work environment, the exposure to formaldehyde occurs by various ways. The gas formaldehyde is absorbed by the respiratory tracts and when in aqueous solution, by cutaneous contact. The effects on health associated with an exposure to this substance vary according to the way of exposure and the concentration or proportions absorptive.

In extreme situations like accidents, it is possible that the formaldehyde is present in the air in strong concentrations, which represents a considerable immediate danger. Concentrations equal or higher than 20 ppm can induce serious pulmonary oedemas and possibly cause death. In the case of a direct contact with the skin, the formaldehyde can involve cutaneous lesions such as irritations, irritating dermites of allergic contact and dermites of contact. The symptoms result in itchings, tinglings and rednesses. A cutaneous sensitizing is likely to appear after a contact with aqueous formaldehyde solutions of concentration equal or higher than 2%, or, solids or resins containing of free formaldehyde. When a person is sensitized, the manifestations of the cutaneous allergy (erythema) are likely to occur with each contact with solutions of increasingly weak concentrations (from formaldehyde 0,5%). These effects are easily avoidable by protecting the exposed areas of the skin, for example, while wearing gloves.

External bonds

INRS : } File | Toxicological card.
international Card of safety (solution at 37%)
Some guides and reports/ratios on the www.irsst.qc.ca site: , and.
Reactions allergic to formaldehyde in dentistry

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