Page:NIOSH Manual of Analytical Methods - 5521.pdf/6

 ISOCYANATES: METHOD 5521, Issue 2, dated 15 August 1994 - Page 6 of 6 SAMPLING MEDIUM Place 25 g 1-(2-methoxyphenyl)piperazine (yellowish white solid) in a 250-mL beaker. Add approximately 125 mL pentane. Bring to a boil (CAUTION: FLAMMABLE) on a hotplate and allow to boil until all but a small amount of yellow oil is in solution. The 1-(2-methoyphenyl)piperazine will melt as it is warmed in the pentane. Decant the solution into a clean beaker, cover with a watchglass and cool in the freezer for 2 to 3 h. White, fluffy crystals will form. Filter with a Buchner funnel. Transfer the crystals to a 50-mL round bottom flask and dry briefly under vacuum to remove final traces of pentane. Store the hygroscopic crystals in an air-tight container in a refrigerator. The melting range of the crystals is 26 to 29 °C. Prepare the sampling medium using the purified 1-(2-methoxyphenyl)piperazine. Dissolve this reagent in toluene at a concentration of 43 µg/mL.

APPENDIX B: PREPARATION OF UREA DERIVATIVE Dissolve 0.005 mole (1 g) of 1-(2-methoxyphenyl)piperazine in 25 mL dimethyl sulfoxide. Dissolve 0.002 mole (350-500 mg) of isocyanate in 25 mL dimethyl sulfoxide. Over a period of 1-2 min, gradually add the isocyanate solution to the stirred derivatizing reagent solution. Warm the resulting solution to 60-90 °C and continue to stir for at least 30 min. Discontinue heating of the solution and add 300 mL deionized water. The urea will precipitate as a white solid. Stop stirring after addition of water. Collect the urea in a fritted-glass Buchner funnel by suction filtration. Dry the compound in a vacuum oven at 75 °C to remove water. Recrystallize until a constant melting point is obtained. To recrystallize urea, add toluene (150 mL) to dried urea and warm mixture to 60 °C. Slowly and very carefully add just enough methanol (BP 65 °C) to completely dissolve the urea. Remove from heat and allow to cool. Collect the crystals by suction filtration and dry them in vacuum oven at 35 °C. The urea derivatives and their melting points are as follows:

Diisocyanate

Urea Derivative

MP (°C)

2,4-TDI

N,N'-bis[4-(2-methoxyphenyl)piperazine-1-carbonyl]2,4-toluenediamine (2,4-TDIU)

212-213 (platelets)

2,6-TDI

N,N'-bis[4-(2-methoxyphenyl)piperazine-1-carbonyl]2,6-Toluenediamine (2,6-TDIU)

231-233 (platelets)

MDI

N,N'-bis[4-(2-methoxyphenyl)piperazine-1-carbonyl]4,4'-methylenedianiline (MDIU)

209-210 (needles)

HDI

N,N'-bis[4-(2-methoxyphenyl)piperazine-1-carbonyl]hexamethylenediamine (HDIU)

199-200 (needles)

NDI

N,N'-bis [4-(2-methoxyphenyl)piperazine-1-carbonyl]1,5-naphthalenediamine (NDIU)

274

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94