Dichloromethane

• Methylene chloride
• Methylene dichloride
• R30

Colorless liquid with a sweet odor

Liquid

1.33 g · cm -3 ( 20 ° C)

-96.7 ° C

39.7 ° C

470 hPa ( 20 ° C)

Poorly in water (20 g · l-1 at 20 ° C)

1.4242 at 20 ° C.

Attention

8.7 (relative to 100 years)

-124.2 KJ / mol

Template: Infobox chemical / molecular formula search available

Dichloromethane ( also methylene chloride, DCM) is an organic chemical compound from the group of chlorinated hydrocarbons with the formula CH2Cl2. Compared to the parent compound methane are therefore substituted by chlorine atoms two hydrogen.

• 5.1 Statements of Decision 455/2009/EC
• 5.2 Reasons for the decision
• 5.3 Criticism of the new legislation

Representation and extraction

Industrially dichloromethane is prepared in a radical substitution by direct reaction of methane and chlorine or methane at a temperature of 400-500 ° C. At this temperature, a gradual radical substitution to carbon tetrachloride takes place:

The result of the process is a mixture of the four chloromethanes, which can be separated by distillation.

Dichloromethane can be dried by refluxing over phosphorus ( or phosphorus -containing drying agents ) and subsequent distillation. Storage of dried dichloromethane via molecular sieve 3 Å = 0.3 nm

Properties

Physical Properties

Dichloromethane is a colorless, flammable liquid with a difficult melting point of -96.7 ° C. The boiling point at normal pressure is 39.8 ° C. The enthalpy of vaporization is 28.82 kJ / mol. It smells sweet, similar to chloroform. The miscibility with water is limited. With increasing temperature, the solubility decreases in dichloromethane water and increases the solubility of water in dichloromethane.

Safety characteristics

Dichloromethane can form flammable vapor -air mixtures. The explosive range is from 13 % by volume (450 g/m3) as the lower explosive limit ( LEL) and 22 vol% (780 g/m3 ) and upper explosive limit (UEL ). The connection can, however, difficult to ignite. This is reflected in the very high minimum ignition energy of 9300 mJ. It could therefore also be measured has no flashpoint. The ignition temperature is 605 ° C. The fabric falls within the temperature class T1. The electrical conductivity is relatively low at 4.3 · 10-9 S · m -1.

Use

Dichloromethane is used as a paint stripper for paints, degreasing and extraction means for caffeine as well as a solvent for resins, fats, plastics and bitumen. In addition, it is used as a refrigerant in refrigeration units.

In the manufacture of polyurethane foams, has for a long time replaced the non-toxic, but ozone depleting refrigerant 1,2-dichloro- 1-fluoroethane (R- 141). Due to the substitution commandment most rigid polyurethane foams are nowadays foamed with water or pentane / cyclopentane in Europe.

In laboratory chemical synthesis is one of the most common solvent dichloromethane in reactions and extractions and is often used as a substitute for the more expensive, and an air and light Phosgenbildung prone chloroform.

In model (eg architecture) it will melt due to its ability to acrylic transparent and easy to connect without the finger, often used as an adhesive. But also for polystyrene occurs in the model used.

In the industry of dichloromethane is also frequently used to bond plastic materials. These include a variety of thermoplastics. Here, the plastic is dissolved and seamlessly " welded ". The following plastics are suitable for sticking with dichloromethane: polystyrene, acrylic glass, polycarbonate, polyethylene and acrylonitrile -butadiene - styrene. Polypropylene and polyethylene can not stick, because they are not soluble.

Safety

When receiving liquid dichloromethane - through the skin - contact causes headache, dizziness, loss of appetite, on the way to anesthesia-like conditions. The vapor is heavier than air. In the combustion of the gaseous dichloromethane, highly toxic phosgene can occur. For dichloromethane is a suspicion of a carcinogenic effect. Dissolved in water it damages small organisms such as Daphnia.

When dealing with dichloromethane protective clothing should be worn including gloves. Latex or nitrile are not sufficient. Instead, gloves should be used Viton or butyl rubber. Butyl gloves should however only be used as a splash guard, as the breakthrough time is 8 minutes. Storage of this compound was carried out in a temperature range of 15 to 25 ° C. Dichloromethane may not come into contact with metallic sodium or other alkali metals, as this can lead to explosions.

Legal situation

The use of dichloromethane in paint strippers was banned by Decision 455/2009/EC of the European Parliament on 6 May 2009 for private and professional use. Exception remains the industry. Preceding this step was to Directive 76/769/EEC, which is replaced by the Neubeschluss and has been included in Annex XVII to Regulation EGREACH. Requirement of this Directive in Germany was the adoption of the Technical Rule 612 " substitutes, replacement procedures and restrictions for use of methylene chloride-based paint stripper".

Statements of Decision 455/2009/EC

The new regulation as EU law, which applies in all European countries, provides for the following restrictions before:

• This affects Stripper, greater than / equal which include dichloromethane in an amount of 0.1 weight percent.
• Prohibition of the first marketing to individuals or business after 6 December 2010.
• Prohibition of sale to private individuals or commercial after 6 December 2011.
• Prohibition of the use by the Trade from 6 June 2012.

Exception of trade, which may continue to use methylene chloride-based paint stripper by a special permit. To this end, the decision provides that the Member States may issue special regulations.

Furthermore, all dichloromethane paint strippers must be explicitly marked for purely industrial use since 6 December 2012.

Reasons for that decision

The decision to ban dichlormethanhaltiger paint stripper by the European Union a major step towards more safety at work has been done. The reasons for this are manifold:

• There is no effective respiratory protection, which can protect against the inhalation of dichloromethane. An effective respiratory protection may be provided only by foreign air masks, which are not to be found in the commercial only in rare cases in the private sector.
• Due to the low boiling point of this substance extremely high concentrations of this chemical are released in the area of the workplace. For measurements was a five-fold, even found a ten-fold excess of the legal limits in areas with poor conditions outdoors.
• Dichloromethane is a suspected mutagenic and to cancer initiation.
• Since the beginning of the use dichlormethanhaltiger Stripper 30 people came to the building industry professional association (BG BAU) in Europe killed. This stems mainly from the fact that dichloromethane is metabolized to carbon monoxide. If ventilation is poor, therefore, threatens suffocation.

Criticism of the new legislation

Dichloromethane in paint strippers can be explained by other chemicals sometimes only poorly, or not at all to replace. Especially in the old nitro - or 2- component paints have today Stripper difficult position. Especially in the field of classic car restoration there are few alternatives. Other methods for color removal are eliminated because of the induced damage.

Also criticized is that besides the grinding removal by heat liberates highly harmful substances.