Isocyanate

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Isocyanate Esters are the general name of various isocyanate esters, which are used in household appliances, automobiles, construction, footwear, furniture, adhesives and other industries. If - NCO Number classification of groups, including mono isocyanate R － N=C=O and Diisocyanate O=C=N-R-N=C=O and Polyisocyanate Etc.

Common diisocyanates include toluene diisocyanate （TDI）、 Isophorone diisocyanate （IPDI）、 Diphenylmethane diisocyanate （ MDI ）、 Dicyclohexylmethane diisocyanate （ HMDI ）、 Hexamethylene diisocyanate （HDI）、 Lysine Diisocyanate (LDI).^[1]

Chinese name: Isocyanate^[2]
Foreign name: Isocyanate
chemical formula: R－N=C=O
molecular weight: forty-three point zero two

Melting point: -86 ℃
Density: About 1.04 ✕ 10 -3 kg/m³
Nature: The general name of various esters of isocyanate
Role: Important Intermediates in Organic Synthesis

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Physical and chemical properties

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Chinese name: isocyanate^[2]

Chinese alias: Isocyanate

English name: isocyanic acid^[2]

English alias: Isocyanic acid; Hydrogen isocyanide；Polyisocyanates;

CAS No ：75-13-8^[2]

Molecular formula: CHNO^[2]

Molecular weight: 43.0247^[2]

Density: 1.04g/cm three^[2]

Boiling point: 39.1 ℃

Flash point: ＜ - 15 ℃ (closed cup)

Autoignition point ：534℃

Vapor pressure ：6750mmHg at 25°C

Appearance: colorless clear liquid with strong irritation.

Solubility : water at 15 ℃ solubility ：1%； 6.7% at 20 ℃.

Usage: used in household appliances, automobiles, construction, footwear, furniture, adhesives and other industries.

Hazard: except stainless steel , nickel, glass, ceramic Other materials There is a risk of corrosion in contact with it. In particular, iron, steel, zinc, tin, copper or their alloys cannot be used as containers.

chemical reaction : Easy and lively hydrogen atom Its compounds: amine, water, alcohol, acid and base react.

Generated by reaction with water Methylamine 、 carbon dioxide ; In the presence of excess water, methylamine reacts with MIC to form 1,3 - Dimethyl urea , forming 1,3,5-trimethyl when excessive MIC Biuret 。 These two reactions are Exothermic reaction 。

In the presence of catalyst, the pure substance undergoes self polymerization and emits heat energy.

Flammable in case of heat, open fire and oxidant. MIC vapor released during combustion nitrogen oxide 、 carbon monoxide and Hydrogen cyanide 。

Pyrolysis at high temperature (350~540 ℃) can form Hydrogen cyanide 。

meet thermal decomposition Release nitrogen oxide smoke.

Preparation method: mainly used in industry Primary amine Isocyanate is produced by phosgene method, and the reaction is as follows: it can be produced by diamine phosgene method Diisocyanate : With the progress of science and technology and the deepening of synthesis theory, Nitro compound The process of synthesizing isocyanate directly with carbon monoxide under high temperature and pressure is becoming more and more mature.

As the isocyanate structure contains unsaturated bonds, it has high activity and is easy to interact with some organic or Inorganic Reaction to produce polyurethane elastomer 。

(1) And Hydroxy compound Reaction of: such as Polyol 、 polyether 、 Polyester amide 、 castor oil And other compounds containing active hydroxyl to generate aminomethyl ester.

(2) With Amino compound Reactions with amine compounds usually produce Substituted urea If further reaction occurs, biuret will be finally formed.

(3) React with water: react with water to form amine and carbon dioxide And amine further reacts with isocyanate to form substituted urea.

(4) With carboxyl Reaction of compound: react with organic carboxylic acid, polyester with carboxyl end group and other compounds Mixed anhydride , and finally decomposes to release carbon dioxide amide 。

(5) And Carbamate Reactions of: reaction generation Urea formate 。

In addition, isocyanate can also undergo self polymerization under appropriate conditions to form Dimer Or high molecular weight polymer, therefore, isocyanates are generally required to be stored at low temperature without light.

purpose

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Monoisocyanate is an important intermediate in organic synthesis, which can be made into a series of Carbamate insecticide , bactericide herbicide It is also used to improve the water resistance of plastics, fabrics, leather, etc. two functional group Isocyanates and above can be used to synthesize a series of excellent Polyurethane foam 、 rubber 、 Elastic fibre , paint, adhesive synthetic leather 、 Artificial wood Etc.

The most widely used and most productive ones are: toluene diisocyanate (Toluene Diisocyanate, short for TDI ）； Diphenylmethane diisocyanate (Methylenediphenyl Diisocyanate, short for MDI ）。

Toluene diisocyanate (TDI) is Colorless Strong pungent liquid, boiling point 251 ° C, specific gravity 1.22, blackened in light, strong to skin and eyes Irritant effect , and can cause eczema And bronchial asthma , mainly for polyurethane Foam plastic, paint synthetic rubber 、 Insulating paint 、 adhesive Etc. According to its composition, toluene diisocyanate is nitrogen-containing Organic compound 。

Diphenylmethane diisocyanate (MDI) is divided into pure MDI and coarse MDI. Pure MDI is a white solid at room temperature, with irritating odor when heated, boiling point 196 ° C, mainly used for polyurethane Rigid foam plastic Synthetic fibre , synthetic rubber, synthetic leather, adhesive, etc. According to its composition, pure diphenylmethane diisocyanate is also an organic compound containing nitrogen groups.

And non yellowing 1,6-Hexanediisocyanate （HDI）。

nature

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Isocyanate A general term for various esters of. There is an isocyanate R-N=C=O and a diisocyanate O=C=N-R-N=C=O. It is generally unpleasant smelling liquid. Isocyanate is easy to react with ammonia or amine to form urea, and easy to react with alcohol to form carbamate (such as Urethane ）。

application

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Used in household appliances, automobiles, construction, footwear, furniture, adhesives and other industries

Production method

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An isocyanate produced by (a) making chlorine And carbon monoxide Reaction production phosgene , (b) make phosgene and Organic amine React to form isocyanate and Hydrogen chloride , (c) separate isocyanate and hydrogen chloride, (d) optionally purify hydrogen chloride, (e) prepare hydrogen chloride aqueous solution, (f) optionally purify hydrogen chloride aqueous solution, (g) make hydrogen chloride aqueous solution electrochemical oxidation Forming chlorine, and (h) returning at least part of the chlorine produced in step (g) to (a).

synthesis

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use Primary amine And carbon disulfide Addition occurs under alkaline conditions, forming Dithiocarbamate After, use P-Toluenesulfonyl chloride Processing, can generate Isothiocyanate 。

scale

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To meet the national energy conservation, environmental protection and Comprehensive utilization of resources Requirements, reasonable realization scale economy The initial scale of a new MDI unit must reach 300000 tons/year or more (reconstruction or Expansion project Except), the initial scale of a new TDI unit must reach 150000 tons/year or more (except for reconstruction or expansion projects).

Some production units of isocyanate Reactor , storage tanks, etc. work under high temperature and pressure, and there are poisoning accidents and fires caused by equipment corrosion or seal leakage Explosion accident And other dangers, which must be strengthened Process , equipment manufacturing and maintenance security management To ensure safe and smooth operation.

1. On phosgene The synthesis unit must be equipped with CO online analyzer methane , hydrogen and other impurities to improve phosgene Synthetic reaction Process safety, guarantee chlorine Moisture is less than 50ppm;

2. For containers, reactors and pumps containing phosgene materials with agitation, double mechanical sealing devices with reliable performance must be used to ensure no phosgene leakage from rotating equipment;

3. For equipment containing phosgene materials, safe Corrosion allowance To avoid corrosion and leakage;

4. For liquid phosgene and liquid storage tanks with phosgene concentration greater than 20%, it is advisable to use pressure charging jacket protection or closed phosgene chamber protection, and for liquid phosgene pipelines, it is advisable to use casing protection, Accident prevention Occurrence of risks;

5. To prevent the danger of system overpressure Key equipment An overpressure discharge valve must be set on the valve to connect with the emergency decomposition system.

poisoning

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Invasion route

Main meridians respiratory tract Inhalation. Because MIC is easy to decompose in water, it is unlikely to enter the blood stream.

toxicology

0.89mg/m for human body three Inhalation for 1-5 minutes, 4 persons Subjects None; 4.46mg/m three 3 patients had tears and nasal irritation; With the increase of the concentration, the irritation symptoms of eyes and respiratory tract gradually became obvious; 46.83mg/m three When the subject felt irritation, he could not bear it.

clinical manifestation

Eye contact and Upper respiratory tract Irritation and damage of: low concentration causes tears and cough , high concentration can cause eye damage Redness and swelling And chemical burns. It can also destroy nasal mucosa , make Anosmia The mucosa of upper respiratory tract may also cause chemical damage. More than 50mg/m three Can cause skin edema, Tissue necrosis 。 Lung damage: the concentration exceeds 50mg/m three Can also cause Chemical pneumonia And pulmonary edema , even cause ARDS 。 Undead often accompany Secondary infection It may cause respiratory distress, Pulmonary function Damaged and can be formed after a long time pulmonary fibrosis 。 When the concentration is very high Bronchospasm Suffocation. In addition, it may cause respiratory tract Anaphylactic reaction , aggravated dyspnea And pulmonary edema. The long-term impact is still difficult to determine. yes India Bhopal Poison Gas Leakage Case Of the victims are still being followed up.

handle

Move the poisoned patients away from the scene quickly. Take off contaminated clothes and observe closely. Supply oxygen when necessary. Eye and Skin contamination Use quickly Flushing with running water 。 Give symptomatic and supportive treatment. Weak if used Lye local Atomization inhalation , early application Glucocorticoid , and available Bronchodilator , antibiotics, etc. In India, someone used an anti edema drug called Lasix, with little effect.

chemical reaction

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RNCO + R′OH → RNHCOOR′

This reaction belongs to Secondary reaction ， reaction rate It changes with the content of hydroxyl group and does not change with the concentration of isocyanate.

Isocyanate with hydroxyl mole ratio , commonly known as isocyanate index , R value.

R value ＞ 1, end NCO sealed Polyurethane prepolymer 。 P-diisocyanate and Diols When R value is greater than 2, the system contains unreacted free isocyanate, which is called semi prepolymer or modified isocyanate.

Example: some elastomer Prepolymer, runway pavement Glue 、 PU Sealants etc.

R value<1, OH terminated prepolymer. mostly Polyurethane adhesive Of Main agent and polyurethane elastomer Raw rubber 。

Example: compound glue polyurethane Ink binder, PU leather paste, tape adhesive, shoe adhesive, etc

R value=1, molecular weight is generated theoretically Infinity Of high polymer In fact, it is impossible due to the influence of moisture and impurities. The closer the R value is to 1, the greater the molecular weight and the greater the viscosity of the system.

Reaction of isocyanate with water

2RNCO + H two O → RNHCONHR + CO two ↑

1 water It is obtained by the reaction of molecule with two NCO groups Substituted urea , water can be regarded as a kind of Chain extender or curing agent 。 This has important guiding significance for the production and storage of polyurethane. The moisture content of raw materials and products should be strictly controlled.

Reaction release carbon dioxide Gas, available in Polyurethane foam In the production, there are also moisture curing polyurethane adhesives and coatings.

Reaction of isocyanate with amino group

RNCO + R′NH two → RNHCONHR′

RNCO + R′NHR〞 → RNHCONR′R〞 Aliphatic group Primary amine The reaction speed is too fast and is seldom used. Aliphatic group Secondary amine Reaction rate with the aromatic primary amine is slightly slow, which is often used to cure prepolymer capped with the NCO.

MOCA, E-300, unilink4200, etc

Different Active hydrogen Reactivity with isocyanate

In theory, isocyanate can react with all compounds that can provide active hydrogen Nucleophilic reaction 。 In compounds containing active hydrogen, nucleophilic Electronic cloud The higher the density is, the stronger its electronegativity is, the higher its reaction activity with isocyanate is, and the faster its reaction speed is.

Aliphatic NH2; Aromatic NH2; Primary OH; Water; Secondary OH; Phenol OH; carboxyl ; Substituted urea; amide ; Carbamate 。

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