**Ecological Production Technology of Phenoxyacetic Herbicides MCPA and 2,4-D in the Highest World Standard**

Wiesław Moszczyński and Arkadiusz Białek *The Institute of Industrial Organic Chemistry, Poland* 

*"Selectivity is a major goal in modern synthetic chemistry" Bartman W., Trost B. M.* 

#### **1. Introduction**

346 Herbicides – Properties, Synthesis and Control of Weeds

STEARMAN, G.K.; LEWIS, R.J.; TORTEROLLI, L.J. & TYLER, D.D. Herbicides reactivity of

STEVENSON, F.J. *Humus chemistry.* Genesis, composition, reactions. 2.ed. New York: John

STEVENSON, F.J. Organic matter reactions involving herbicides in soil.

TESTA, B. 1995. The metabolism of drugs and other xenobiotcs. Academic Press, New York.

THEISEN, G.; VIDAL, R. A.; FLECK, N. G. Redução da infestação de*Brachiaria* 

THEISEN, G; VIDAL, R. A. (1999). Efeito da cobertura do solo com resíduos de aveia preta

TRAGETTA, D.G.; VAZ, C.M.P.; MACHADO, S.A.S.; VIEIRA, E.M.; MARTIN-NETO, L.

VIDAL, R.A.; THEISEN, G.; FLECK, N.G.; BAUMAN, T.T. Palha no sistema de semeadura

WEIR, T.L., S.W. PARK AND J.M VIVANCO. 2004. Biochemical and physiological

WICKS, G.A.; CRUTCHFIELD, D.A.; BURNSIDE, O.C. Influence of *wheat (Triticum aestivum*)

YU, J.Q., S.F. YE, M.F. ZHANG AND W.H. HU. 2003. Effects of root exudates and aqueous

polarográficos. *Comunicado Técnico,* São Carlos, n.14, p. 1-7, dez. 1996. VAZ DE MELO, A. GALVÃO, J.C.C., FERREIRA, L.R. , MIRANDA, G.V. , TUFFI SANTOS,

tradicional. *Planta Daninha*, Viçosa, MG, v. 25, n.3, p. 521-527.

*plantaginea* em soja pela cobertura do solo com palha de aveia preta. *Pesquisa* 

nas etapas do ciclo de vida do capim-marmelada. *Planta Daninha*, v. 17, n.2, p.189-

Mecanismos de sorção da atrazina em solos: estudos espectroscópicos e

L.D., SANTOS, I.C. e SOUZA, L.V. (2007). Dinâmica populacional de plantas daninhas no cultivo de milho-verde no sistema de plantio direto orgânico e

direta reduz a infestação de gramíneas anuais e aumenta a produtividade da soja.

mechanisms mediated by allelochemicals. *Current Opinion* in *Plant Biology,*

straw mulch and metalachlor on corn (*Zea mays*) growth and yield. *Weed Science*,

root extracts of cucumber (*Cucumis sativus*), and allelochemicals on photosynthesis and antioxidant enzymes in cucumber. *Biochemical Systematics and Ecology*.

*America Journal*, 53:1690-1694, 1989.

*Journal of Environmental Quality*, 1:333-343, 1972.

*Agropecuária Brasileira*, v. 35, p. 753-756, 2000.

*Revista Científica Rural*, v.28, p. 373-377, 1998.

Willey & Sons, 1994. 443p.

475p.

196.

7(4):p.472-479.

31(2):129-139.

v.42, p.141-147, 1994

soil organic matter fractions in no-tilled and tilled cotton. *Soil Science Society of* 

Herbicides MCPA (4-chloro-2-metylphenoxyacetic acid) and 2,4-D (2,4-dichlorophenoxyacetic acid), which belong to the group of chlorophenoxyacetic acids, have been produced in Poland since the break of the sixties in the scale of many thousands of tons per year, which constitutes 5-7% of the world's production. Acids and their salts are exported to all continents. An advantage of herbicides within this group is their harmlessness for man and environment in doses used in agriculture. The condition is the high content and purity of the active substance in utility preparations. Unfortunately, classic technologies based on the reaction of phenols chlorination or their derivatives used until today all over the world do not ensure high purity, and significant quantities of highly toxical chloroorganic waste compounds originate in the production process. The main cause lies in the low selectivity of the reaction of chlorination of phenols' aromatic ring. Numerous producers enrich the purity of chlorophenols with the method of rectification. As our research has shown, in the process of rectification and while burning post-rectification wastes, dioxines and dibenzofurans can originate.

Below we present research conducted in the Institute of Industrial Organic Chemistry (IPO) in Warsaw with strict cooperation with production plants "Rokita Agro" in Brzeg Dolny and "Organika Sarzyna" in Nowa Sarzyna over the development of technologies of chlorophenoxyacetic herbicides. Commonly used "classical" technologies of production of MCPA and 2,4-D are based on two subsequent reactions – chlorination of phenol or 2 methylphenol and the reaction of the obtained chlorophenol with chloroacetic acid (MCAA), commonly called condensation. The first stage – chlorination reaction – is critical for the nature of the entire reaction, i.e. the number of operations, selection of equipment, purification methods, wastes. Electrophilic reaction of chlorination of aromatic phenol ring is non-selective. Isomers and polychlorinated compounds are always originated. In order to increase the selectivity of reaction and the purity of the the final product, various technologies of chlorination and purification of chlorophenols are used all over the world,

Ecological Production Technology

the reaction is presented below.

OH

CH3

+ ClCH2COOH

commonly used by chemical companies all over the world.

2-methylphenol 2-methylphenoxyacetic acid

of Phenoxyacetic Herbicides MCPA and 2,4-D in the Highest World Standard 349

with that 40% of waste chloromethylphenols was originated. The preparation Chwastoks R-30 had a good opinion among its users. It did not freeze in winter in unheated warehouses, it perfectly dissolved in water. It was cheap. In IPO a comparative research of the activity of MCPA-70 with pure MCPA was conducted, and the activity of each chloromethylphenoxyacetic acids separately, and also their mixtures. It appeared that isomeric 6-chloro-2-methylphenoxyacetic acid had a high biological activity, and in the mixtures the synergism of activity was observed. After 10 years of MCPA-70 production in a small installation in 1972 a new production facility of 4500 tons per year capacity was started without substantial changes in technology. In the discussed decade in the European market there appeared MCPA preparations of high purity, without free chloromethylphenols containing 80-90% of the pure active component. In the technologies sulfuryl chloride was used as a more selective chlorinating agent, and sometimes additionally vacuum rectification of technical 4-chloro-2-methylphenol. Chemische Werke Schwarzweide in GDR started the production of MCPA basing on sulfuryl chloride on the license purchased in Great Britain. The technology based on sulfuryl chloride is currently

Skeeters was the first to describe in 1956 the MCPA synthesis through chlorination of 2 methylphenoxyacetic acid (MPA) in 1,2-dichloroethane (Skeeters et al., 1956). In the seventies such a method was used in industry. It was a new generation technology, below referred to as the reverse method, and the obtained product – "MCPA 90". The diagram of

(MPA)

The aromatic ring of MPA acid is less prone to electrophilic substitution, and the side chain is a steric hindrance for creating the isomer 6-chloro-. In the reaction of MPA, chlorination selectivity of 80-90% is achieved, i.e. higher than in the classical method, where sulfuryl chloride without purification of the product by rectification is used. In the reverse technology a barrier which is difficult to lift is the high melting temperature of MPA (157ºC) and the low solubility (7%) in organic solvents. Chlorination of MPA acid without solvents in hot water cannot be performed to the end and there remains 20% of non-chlorinated MPA. In Bratysława, the chlorination of 20-30% of water solution of MPA sodium salt MPA in the temperature of 90-100 ºC was used on the industrial scale. The final product, containing 90% of the active substance, contained 5% of isomer 6-chloro- and 3-6% of free MPA (Rapoš et al, 1960). Chimzawod in Ufa, USSR, launched a multi-ton installation of MPA acid chlorination in 7% solution in solvent. The license with the full equipment was purchased from the Fisons company (Great Britain). The MCPA purity was 85-90%, the

product contained 1-3% of free MPA, efficiency about 92% (Moszczyński, 1971).

+ Cl2 CH3 Cl

OCH2COOH

MCPA

CH3

OCH2COOH

including regioselective catalysts, replacement of chlorine with sulfuryl chloride, rectification of chlorophenol and reversed technologies, i.e. condensation first, and then chlorination of the obtained phenoxyacetic acid. Also in our country technologies of production of MCPA and 2,4-D have been changed many times, achieving higher and higher selectivity of the chlorination reaction. The current production of MCPA (Chwastoks) is based on a unique technology of chlorination of 98% selectivity, while in the 2,4-D technology 96% selectivity has been achieved, and after crystallization it ensures the purity of the product equal to 98%. Technologies minimize or eliminate waste chloroorganic compounds. The final products have the highest quality standard.
