Methylene diphenyl diisocyanate
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| 4,4'-methylene diphenyl diisocyanate | |
|---|---|
| Image:4,4'-methylene diphenyl diisocyanate.svg | |
| Image:Methylene-diphenyl-diisocyanate-3D-vdW.png | |
| IUPAC name | 1-isocyanato-4- [(4-isocyanatophenyl)methyl] benzene |
| Other names | Pure MDI 4,4'-methylene diphenyl diisocyanate 4,4'-diphenylmethane diisocyanate |
| Identifiers | |
| CAS number | |
| RTECS number | NQ9350000 |
| SMILES | O=C=NC(C=C2)=CC=C2C C1=CC=C(N=C=O)C=C1 |
| Properties | |
| Molecular formula | C15H10N2O2 |
| Molar mass | 250.25 g/mol |
| Appearance | white or pale yellow solid |
| Density | 1.230 g/cm3, solid |
| Melting point |
40 °C (313 K) |
| Boiling point |
314 °C (587 K) |
| Solubility in water | Reacts |
| Hazards | |
| EU classification | Harmful (Xn) |
| R-phrases | R20, R36/37/38, R42/43 |
| S-phrases | (S1/2), S23, S36/37, S45 |
| Flash point | 212–214 °C (Cleveland open cup) |
| Related Compounds | |
| Related Isocyanates | Toluene diisocyanate Naphthalene diisocyanate |
| Related compounds | Polyurethane |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
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Overview
Methylene diphenyl diisocyanate, most often abbreviated as MDI, is an aromatic diisocyanate. It exists in three isomers, 2,2'-MDI, 2,4'-MDI, and 4,4'-MDI. The 4,4' isomer is most practically useful, and is also known as Pure MDI. MDI is reacted with a polyol in the manufacture of polyurethane. It is the most produced diisocyanate, accounting for 61.3% of the global market in the year 2000.[1]
Synthesis
There are six steps to the manufacture of pure 4,4'-MDI:[1]
- Nitration: Reaction of benzene with nitric acid and a catalyst, to form nitrobenzene
- Hydrogenation: Reaction of the nitrobenzene with hydrogen and a catalyst, to form aniline
- Aniline/Formaldehyde condensation: Reaction of the aniline with formaldehyde and a catalyst, to form methylene dianiline (MDA), also known as diaminodiphenylmethane (DADPM)
- Phosgenation: Reaction of the MDA/DADPM with phosgene, to form an MDI mixture
- Separation: Distillation of the MDI mixture to form Polymeric MDI (a mixture of oligomeric polyisocyanates) and a MDI isomer mixture which has a low 2,4' isomer content
- Purification: Fractionation of the MDI isomer mixture to form pure 4,4'-MDI and an MDI isomer mixture which has a high 2,4' isomer content
Chemistry
The positions of the isocyanate groups influences their reactivities. 4,4'-MDI is a symmetrical molecule and thus has two groups of equal reactivity. 2,4'-MDI is an asymmetrical molecule and thus has two groups of different reactivities. The group at the 4-position is approximately four times more reactive than the group at the 2-position.[1]
Production
Major producers include Bayer, Dow, Huntsman, Elastogran, Repsol, Shell Chemicals, and Tosoh. Total world production of MDI and polymeric MDI is over 2 million tonnes per year (Mt/a).
Uses
4,4'-MDI has one major application, that is the production of rigid polyurethane. Typically, one tonne of polyurethane foam needs 0.616 tonne of MDI and 0.386 tonne of polyol, with 0.054 tonne pentane as a blowing agent. These rigid polyurethane foams are good thermal insulators and used in nearly all freezers and refrigerators worldwide, as well as buildings. Typical polyols used are polyethylene adipate (a polyester) and poly(tetramethylene ether)glycol (a polyether).
4,4'-MDI is also used as an industrial strength adhesive, which is available to end consumers as various high-strength bottled glue preparations.
Safety
MDI is the least hazardous of the commonly available isocyanates, as it has a very low vapour pressure. This reduces its hazards during handling compared to the other major isocyanates (TDI, HDI). However, it, like the other isocyanates, is an allergen and sensitizer. Persons developing sensitivity to isocyanates may have dangerous systemic reactions to extremely small exposures, including respiratory failure. MDI should be not be heated or sprayed except with strict engineering controls and personal protective equipment. It has low human toxicity. It is a reactive material and reacts with hydrogen donors, in some cases violently. Its reaction with water produces carbon dioxide which can burst containers and produce aerosols. Since it polymerizes in the presence of water, its ecological risks are low.
See also
References
- ↑ 1.0 1.1 1.2 Randall, David; Lee, Steve (2002). The Polyurethanes Book. New York: Wiley. ISBN 0-470-85041-8.
External links
- NIOSH Safety and Health Topic: Isocyanates, from the website of the National Institute for Occupational Safety and Health (NIOSH)
- Hazards of TDI, MDI, and HDI
- Isofact American Chemistry Council Diisocyanates Panel
- Azom Chemical database on Polyurethane chemistry
nl:Methyleendifenyldi-isocyanaat
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
