Applications of Organic Tin Compounds

Introduction

Organic tin compounds are compounds based on tin with hydrocarbon substituents. This field grew rapidly in the 20th century, especially after the Grignard reagents were found that can be used to produce Sn-C bonds. Organic tin compounds have a wealth of applications in the continuing activities of industrial and research laboratories. This article will briefly introduce the the usage of arganic tin compounds as catalysts and thermal stabilizers.

 

Applications

1 As Catalysts

Organotin catalysts are currently the most widely used metal catalysts in polyurethanes, and there are many domestic and foreign manufacturers. Organotin catalysts have good catalytic activity in both polyurethane prepolymerization and film curing. The main organotin catalysts on the market are dibutyltin dilaurate (DBTDL) and stannous octoate. Organotin compounds can coordinate with isocyanate to polarize -NCO, thus making the positively charged carbon atoms in the isocyanate molecule more active and more susceptible to the hydroxyl end of the polyol polymer. In the synthesis of polyurethanes, although the tertiary amine catalysts have a certain catalytic effect on the reaction of -NCO/-OH, they have a stronger catalytic effect on the reaction of -NCO/H2O. Organotin can also exhibit a strong catalytic effect on the -NCO/-OH reaction.

 

The catalytic activity of organotin catalysts is related to their molecular structure. The order of activity is as follows: R2SnX2>R2SnO, R2SnS>RSnX3=RSnOOH=R3SnX>R4Sn. For organotin catalysts containing different substituents R and X, the order of their catalytic activity is as follows: R is -CH3> -C4H9> -C6H5; while X is -OH> -OC4H9 = -SC4H9 = -OCOCH3> Cl>F.

 

2 As Thermal Stabilizers

Organotin thermal stabilizers have good thermal stability, weatherability and transparency, so they are one of the most widely used and effective thermal stabilizers. The consumption of organic tin heat stabilizers in the United States accounted for 28% of the total, while Japan and Europe reached 25% and 18% respectively.

 

It has been reported that there are thousands of organotin compounds that can be used as heat stabilizers for PVC, but no more than 20 have been widely used commercially. These commercial organotin heat stabilizers are all tetravalent tin compounds with the general chemical structure Rn-Sn-X4-n. In this structure, n is 1 or 2; R is methyl, n-butyl, n-octyl or ester; X is a mercaptocarboxylate, maleate or fatty acid radical. Organotin-based heat stabilizers are generally classified into ester-based mercaptan organotin, retrosteryl mercaptan organotin, maleate organotin, and fatty acid organotin in terms of X. The stabilizing effect and characteristics of organotin heat stabilizers with different structures are obviously different.

 

Organotin thermal stabilizers are divided into one-component organotin heat stabilizers and composite organotin heat stabilizers according to their compositional complexity. Organic tin heat stabilizers generally have outstanding advantages such as high thermal stability and excellent transparency. However, single-component organic tin heat stabilizers have their own disadvantages. For example, organotin tin mercaptans have excellent thermal stability performance, while its lubricating processability is poor. The thermal stabilizing performance of fatty acid organotin is far inferior to that of organotin tin mercaptans, but its lubricating processability is excellent. Therefore, in order to improve the cost-effectiveness of organotin heat stabilizers and to compensate for the respective performance deficiencies of single-component organotin heat stabilizers, the development of composite organotin heat stabilizers has received increasing attention in recent years. The composite organotin heat stabilizer refers to a heat stabilizer composed of two or more organotin compound components, or at least one organotin compound component and one or more other compound components, wherein The other compound components may be selected from organic metal salt heat stabilizers, organic auxiliary heat stabilizers, antioxidants, or lubricants.

 

Conclusion

Organotin compounds are currently mainly used as catalysts such as dibutyltin, stannous octoate; stabilizers such as dimethyltin, dioctyltin, tetraphenyltin; fungicides and agricultural pesticides such as DBT, tributyltin, triphenyltin.


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