3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide 

3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide

C₁₀H₁₂N₂O₃S

Colourless crystals.

138 ℃.

0.17 mPa (20 ℃).

1.41 (20 ℃).

In water 570 mg/l (pH 7, 20℃ ). In acetone 1387, methanol 1061, ethyl acetate 582, dichloromethane 206, n-heptane 0.5 ×10^-3 (all in g/l, 20 ℃).

Very resistant to hydrolysis in both acidic and alkaline media. Decomposed by sunlight.

3.3 (24 ℃) 

Photosynthetic electron transport inhibitor at the photosystem II receptor site.

Selective contact herbicide, absorbed mainly by the foliage, with very little translocation, but also absorbed by the roots, with translocation acropetally in the xylem.

A contact herbicide controlling Anthemis, Chamomilla and Matricaria spp., Chrysanthemum segetum, Galium aparine, Lapsana communis and Stellaria media in winter and spring cereals, at 1.0-2.2 kg/ha. Other crops include peanuts, maize, peas, Phaseolus beans, rice (Cyperus difformis, C. esculentus, C. serotinus, Monochoria vaginalis, Sagittaria pygmaea, S. sagittifolia, Alisma and Commelina spp., Scirpus maritimus and S. mucronatus) and soya beans (Abutilon theophrasti, Capsella bursa-pastoris, Cyperus esculentus, Datura stramonium, Helianthus spp., Polygonum spp., Portulaca spp., Sida spinosa, Ambrosia spp., Sinapis arvensis and Xanthium spp.).

FAO/WHO 83, 85, 86 (see part 2 of the Bibliography).

Acute oral LD₅₀ for rats >1000, dogs >500, rabbits 750, cats 500 mg/kg.

Acute percutaneous LD₅₀ for rats >2500 mg/kg. Moderately irritating to skin and eyes (rabbits).

LC₅₀ (4 h) for rats >5.1 mg/l air.

(1 y) for dogs 13.1 mg/kg b.w.; (2 y) for rats 10 mg/kg b.w.; (90 d) for rats 25, dogs 10 mg/kg b.w.; (78 w) for mice 12 mg/kg b.w.

(JMPR) 0.1 mg/kg [1998, 1999].

WHO (a.i.) III; EPA (formulation) III

Acute oral LD₅₀ for bobwhite quail 1140 mg/kg. Dietary LC₅₀ for bobwhite quail and mallard ducks >5000 ppm.

LC₅₀ (96 h) for rainbow trout and bluegill sunfish >100 mg/l.

LC₅₀ (48 h) 125 mg/l.

EC₅₀ (72 h) for green algae (Ankistrodesmus) 47.3 mg/l.

EC₅₀ (14 d) >1000 mg/kg soil.

In plants, rapidly metabolised to derivatives of anthranilic acid, the principal metabolites being the 6- and 8-hydroxy derivatives, which are conjugated to sugars, forming glycosides.

Metabolism studies in three different species showed that bentazone was only poorly metabolised, the parent compound being the predominant product. Only small amounts of hydroxylated bentazone metabolites could be detected. No conjugated products were found.

In soil, short-lived hydroxy compounds are first formed, which rapidly undergo further degradation (R. Huber & S. Otto in Rev. Environ. Contam. Toxicol., 137, 111-134). In sunlight, bentazone undergoes rapid degradation, ultimately to CO₂. It has low soil persistence: in freshly collected field soils, aerobic DT₅₀ (lab., 20 篊) was 14 d. In lab. degradation studies, with soils of proven biological activity, DT₅₀ (average) was 17.8 d; DT₅₀ (field, average) was c. 12 d; corresponding DT₉₀ was 44 d. Koc 13.3-176 ml/g (average 42 ml/g), indicating mobility. However, when used according to good agricultural practice, bentazone is degraded more quickly than it can leach; in all lysimeter studies, average annual leachates contained <0.1 mg/l. 

analysis by rplc with u.v. detection (AOAC Methods, 17th Ed., 993.02; CIPAC Handbook, 1985, 1C, 1973) or by glc of a derivative.