Petroleum Markers Synthesized from n-alkylbenzene and Aniline Derivatives

Transcription

1 5054 Ind. Eng. Chem. Res. 2003, 42, Petroleum Markers Synthesized from n-alkylbenzene and Aniline Derivatives Somsaluay Suwanprasop, Sasitorn Suksorn, Thumnoon Nhujak, Sophon Roengsumran,, and Amorn Petsom*,, Program of Petrochemistry and Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Petroleum markers 1-20 were synthesized either by a coupling reaction of n-alkylaniline (which was prepared from nitration and reduction reactions of n-alkylbenzene) with a diazonium salt of aniline derivatives or by a coupling reaction of a diazonium salt of n-alkylaniline with aniline or phenol derivatives. These synthetic markers provided invisible color in high-speed diesel fuel at an effective usable level (3-5 ppm), but gave visible colors when detected by extraction with 50% (v/v) 1,2-diaminoethane in a solution containing propane-1,3-diol and methanol (2:3, v/v). Marker contents in fuel oil could be successfully quantified with a VIS spectrophotometer. The markers did not alter the physical properties of the diesel fuel (as revealed by tests performed according to ASTM methods), and they were also stable in diesel fuel over a period of at least 3 months, suggesting that these synthetic dyes could readily be applied as petroleum markers in commercial fuel oils. I. Introduction At present, large quantities of fuel oils are consumed for various applications throughout the world. As a whole, fuel oils are taxed according to government rates, which are dependent on the types and purposes of the fuel oils. Differences in taxation have caused governments to lose considerable revenue to fraud, for instance, smuggling of untaxed oil, mixing of oil taxed at a high rate with that taxed at a low rate, and mixing of hydrocarbon solvents into fuel oils. To prevent these problems, marker systems have been suggested as means to identify brands of fuel and to monitor the tax classification of petroleum products. Marker systems for fuel oils and petroleum products have been reported and used for a long time. 1 Several marker dyes have been successfully established, including isobenzofuranones, 2 quinizarin derivatives, 3 2-naphthylamine derivatives, 4 substituted 1,4-dihydroxyanthraquinones, 5 azo compounds, 6,7 and fluorescent markers such as phthalocyanines and naphthocyanines This paper reports on the synthesis of petroleum markers from n-alkylbenzene (10-14 carbon atoms in the alkyl side chain) and aniline or phenol derivatives. n-alkylbenzene was converted to n-alkylaniline by nitration and reduction reactions. n-alkylaniline was subsequently transformed into marker dyes by two methods: first, by coupling with a diazonium salt of aniline derivatives and, otherwise, by conversion to a diazonium salt followed by coupling with aniline or phenol derivatives. These synthetic petroleum markers provided invisible color in liquid petroleum products at an effective usable level, but gave distinctive colors when extracted from the petroleum products into an appropriate basic reagent. In addition, the basic * To whom correspondence should be addressed. Mail: Dr. Amorn Petsom, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand. Tel.: Fax: amorn.p@ chula.ac.th. Program of Petrochemistry. Department of Chemistry. reagent used for extraction is easy to handle and readily applied for the rapid detection of petroleum markers in fuel oils. II. Experimental Section Materials and Methods. n-alkylbenzene was obtained as a commercial product and used without further purification. All reagents were of analytical grade from Fluka. Thin-layer chromatography was performed on aluminum sheets precoated with silica gel (Merck Kieselgel 60 F 254 ). Column chromatography was performed on silica gel (Merck Kieselgel 60 G). The infrared spectra were recorded on a Nicolet (Impact 410) FT-IR spectrophotometer. The 1 H and 13 C NMR spectra were obtained with a Bruker (ACF200) spectrometer, operating at MHz for 1 H and MHz for 13 C. ESITOF MS were obtained with a Micromass (LCT) mass spectrometer. The quantities of markers in the diesel fuels were measured using a Perkin-Elmer (Lambda 2) VIS spectrophotometer. The flash points (Pensky-Martens) of the marked and unmarked diesel fuels were measured in an ISL (PMFP93) flash point analyzer, and the pour points of the marked and unmarked diesel fuels were recorded on an ISL (CPP92) pour point analyzer. The kinematic viscosities of the marked and unmarked diesel fuels were recorded on a Cannon viscometer. The sulfur contents of the marked and unmarked diesel fuels were determined employing a Perkin-Elmer (Antex9000) CHNS/O analyzer. The distillations of the marked and unmarked diesel fuels were performed with a Herzog (MP626) distillation apparatus. The total acidities of the marked and unmarked diesel fuels were evaluated with a Metrohm 665 total acid number analyzer, and the colors of the marked and unmarked diesel fuels were observed with a Lovibond (PFX990/P) petrochemical tintometer. Preparation of 1-Nitro-4-n-alkylbenzene. Concentrated sulfuric acid (40.0 ml, 0.72 mol) was added in portions to concentrated nitric acid (35.0 ml, 0.50 mol); the mixture was vigorously stirred, and its tem /ie020472h CCC: $ American Chemical Society Published on Web 09/18/2003

2 Ind. Eng. Chem. Res., Vol. 42, No. 21, perature was kept at 5 C using an ice bath. n- Alkylbenzene (49.30 g, 0.20 mol; calculation based on C 12 H 25 for the alkyl side chain) was added slowly into the above mixed acids while the reaction temperature was held at temperatures between 0 and 5 C. The mixture was continually stirred for 1 h, after which it was diluted with 500 ml of cold water, and the two phases were separated. The yellow liquid product was washed with 20 ml of cold water (2-3 times), and unreacted n-alkylbenzene was removed by silica gel column chromatography eluted with n-hexane. 1-Nitro- 4-n-alkylbenzene (49.50 g, 85% yield) was obtained as a yellow liquid, which was characterized by analyses of FT-IR, ESITOF MS, and 1 H and 13 C NMR spectral data. Preparation of 4-n-Alkylphenylamine. 11 A mixture of 1-nitro-4-n-alkylbenzene (49.50 g, 0.17 mol) and tin (45.00 g, 0.38 mol), which was placed in a flask equipped with a reflux condenser, was stirred, and then 10 ml of concentrated hydrochloric acid was added dropwise. Because this reaction is exothermic, the flask was dipped into a cold-water bath to control the reaction temperature. When the initial reaction had subsided, another 10 ml of acid was added to the reaction mixture. This process was repeated until a total of 90 ml (1.08 mol) of acid had been added. An aqueous sodium hydroxide solution (125.0 ml, 15 M) was gradually added into the mixture. An oily liquid product was then extracted with n-hexane, yielding a colorless liquid of 4-n-alkylphenylamine, which was characterized by analyses of FT-IR, ESITOF MS, and 1 H and 13 C NMR spectral data. Preparation of Petroleum Markers. Aniline derivatives employed in the synthesis of petroleum markers groups A and B were 4-nitroaniline, 2-nitroaniline, 4-chloro-2-nitroaniline, 4-chloro-3-nitroaniline, 2-chloro- 4-nitroaniline, 2-chloro-5-nitroaniline, and 2-methoxy- 4-nitroaniline. Preparation of Petroleum Marker Groups A and B (Compounds 1-14). For the synthesis of markers in group A (1-7; structures shown in Figure 1), aniline derivative (0.01 mol) was added to a mixture of concentrated hydrochloric acid (3 ml) and water (3 ml). The mixture was stirred vigorously while being cooled to 0 C, and a solution of sodium nitrite (0.69 g, 0.01 mol) in distilled water (20 ml) was added dropwise to the reaction mixture. When the pale yellow solution of benzenediazonium was obtained, this solution was added dropwise into a phenylammonium ions solution while the temperature of the reaction mixture was kept at 0 C. The solution of phenylammonium ions was prepared by dissolving n-alkylaniline (2.61 g, 0.01 mol) in methanol (20 ml) containing sodium acetate (0.62 g, mol). The reaction mixture was stirred at temperatures between 0 and 5 C for 1 h. The marker product was extracted from the reaction mixture with dichloromethane. The dichloromethane layer was washed repeatedly (3-4 times), each time with 20 ml of distilled water, and then evaporated to dryness. The crude product was purified by silica gel column chromatography, eluted by a mixture of n-hexane and dichloromethane (3:1). The common yield of each marker was 60-80%. Petroleum markers were individually characterized by spectroscopic techniques (FT-IR, ESITOF MS, and 1 H and 13 C NMR). Assignments of proton ( 1 H) and carbon ( 13 C) NMR of markers 1-7 are provided in the Supporting Information. For markers in group B (8-14; structures shown in Figure 1), n-alkylaniline (2.61 g, 0.01 mol) was added to a mixture of concentrated hydrochloric acid (3 ml) and methanol (3 ml). The mixture was stirred vigorously while being cooled to 0 C, and a solution of sodium nitrite (0.69 g, 0.01 mol) in distilled water (20 ml) was added dropwise to the reaction mixture. When the pale yellow solution of n-alkylbenzenediazonium was obtained, this solution was added dropwise into an arylammonium ions solution while the temperature of the reaction mixture was kept at 0 C. The solution of arylammonium ions was prepared by dissolving aniline derivative (0.01 mol) in methanol (20 ml) containing sodium acetate (0.62 g, mol). The reaction mixture was stirred at temperatures between 0 and 5 C for 1 h. Each marker dye product was extracted and worked up in the same manner as used for the markers in group A. The common yield of each marker was 55-70%. Petroleum markers were individually characterized by spectroscopic techniques (FT-IR, ESITOF MS, and 1 H and 13 C NMR). Assignments of proton ( 1 H) and carbon ( 13 C) NMR of markers 8-14 are provided in the Supporting Information. Preparation of Petroleum Marker Group C (Compounds 15-20; structures shown in Figure 1). Phenol and its derivatives employed in the synthesis of petroleum markers in group C were phenol, benzene-1,3-diol, benzene-1,2-diol, 2,6-di-tert-butylphenol, naphthalen-1- ol, and naphthalen-2-ol. n-alkylbenzenediazonium was prepared in the same manner as used for marker groups A and B. When the pale yellow solution of n-alkylbenzenediazonium was obtained, this solution was added dropwise into a phenolate ion solution while the temperature of the reaction mixture was kept at 0 C. The solution of phenolate ions was prepared by dissolving phenol or its derivative (0.01 mol) in methanol (20 ml) containing potassium hydroxide (0.84 g, mol). The reaction mixture was stirred at temperatures between 0 and 5 C for 1 h. Each marker product was extracted and purified in the same manner as used for marker groups A and B. The common yield of each marker was 70-80%. Petroleum markers were individually characterized by spectroscopic techniques (FT-IR, ESITOF MS, and 1 H and 13 C NMR). Assignments of proton ( 1 H) and carbon ( 13 C) NMR of markers are provided in the Supporting Information. Suitable Extraction System for the Detection of Petroleum Markers in Diesel Fuel. To determine the suitable extraction system for the detection of petroleum markers, the marker 2-(4 -nitro-phenylazo)-4-n-alkylphenylamine (1) was used as a marker model because its color in the extracted phase was red, which is easily observed. Diesel fuel containing 10 ppm of marker 1 was employed for the determination of the suitable extraction system. The marked diesel fuel (30 ml) was pipetted into a 50-mL screw cap vial. Subsequently, 5 ml of each extraction system was added into a separate vial, each of which was capped and shaken for 30 s. The extraction systems were 10% (v/v) hydrochloric acid, 10% (v/v) formic acid, 10% (v/v) acetic acid, 1-5% (w/v) potassium hydroxide, 10-50% (v/v) diethylamine, and 10-50% (v/v) 1,2-diaminoethane in a solution containing propane-1,3-diol and methanol (2:3, v/v). The mixtures were left at room temperature until two phases were observed. The lower phase, which developed color, was drawn off for recording the maximum absorption in the

3 5056 Ind. Eng. Chem. Res., Vol. 42, No. 21, 2003 Figure 1. Structures of petroleum markers visible region for λ ) nm using a VIS spectrophotometer. The extraction system that gave the highest absorption at its maximum wavelength (λ max ) was regarded as the suitable extraction system. Efficiency of Extraction Systems. The efficiency of each extraction system was studied by comparing the amount of marker in the extracted phase with the amount originally added to the diesel fuel, employing 2-(4 -nitro-phenylazo)-4-n-alkylphenylamine (1) as a marker model. Diesel fuel containing 4 ppm of marker 1 was employed for the determination of the efficiencies of the extraction systems. The marked diesel fuel (30 ml) was pipetted into a vial, and 5 ml of 50% (v/v) 1,2- diaminoethane in a solution containing propane-1,3-diol and methanol (2:3, v/v) was added. The reaction vial was capped and shaken for 30 s. The VIS absorption (at λ max of the extraction system) of the lower phase was measured, and the concentration of marker 1 in the extraction phase was determined by comparing the observed absorbance with the calibration curve. This obtained marker content led to the calculation of the weight and percent of extraction.

4 Table 1. VIS Absorbance of the Alcohol Part from Extraction of Compound 1 with Various Solvent Systems a extraction system Ind. Eng. Chem. Res., Vol. 42, No. 21, λ max visual (nm) absorbance b color time to separate (min) b Acidic Systems A1. 10% (v/v) HCl in PD c /MeOH (2:3, v/v) N/A d N/A dark yellow 7.08 ( 0.08 A2. 10% (v/v) HCOOH in PD/MeOH (2:3, v/v) N/A N/A dark yellow 7.03 ( 0.06 A3. 10% (v/v) CH 3COOH in PD/MeOH (2:3, v/v) N/A N/A dark yellow 7.15 ( 0.06 Basic Systems B1. 1% (w/v) KOH in PD/MeOH (2:3, v/v) ( red ( 0.07 B2. 2% (w/v) KOHin PD/MeOH (2:3, v/v) ( red ( 0.05 B3. 3% (w/v) KOHin PD/MeOH (2:3, v/v) ( red ( 0.07 B4. 4% (w/v) KOHin PD/MeOH (2:3, v/v) ( red 8.15 ( 0.07 B5. 5% (w/v) KOHin PD/MeOH (2:3, v/v) ( red 8.19 ( 0.05 B6. 10% (v/v) DEA e in PD/MeOH (2:3, v/v) ( red 6.10 ( 0.06 B7. 20% (v/v) DEA in PD/MeOH (2:3, v/v) ( red 6.06 ( 0.05 B8. 30% (v/v) DEA in PD/MeOH (2:3, v/v) ( red 6.04 ( 0.04 B9. 40% (v/v) DEA in PD/MeOH (2:3, v/v) ( red 6.12 ( 0.03 B10. 50% (v/v) DEA in PD/MeOH (2:3, v/v) ( red 6.04 ( 0.06 B11. 10% (v/v) DAE f in PD/MeOH (2:3, v/v) ( red 6.07 ( 0.01 B12. 20% (v/v) DAE in PD/MeOH (2:3, v/v) ( red 6.12 ( 0.06 B13. 30% (v/v) DAE in PD/MeOH (2:3, v/v) ( reddish-purple 6.07 ( 0.06 B14. 40% (v/v) DAE in PD/MeOH (2:3, v/v) ( purple 6.03 ( 0.05 B15. 50% (v/v) DAE in PD/MeOH (2:3, v/v) ( purple 6.11 ( 0.03 a Compound 1 in diesel fuel (10 ppm) was a marker model. b Average ( standard deviation, n ) 3. c Propane-1,3-diol (PD). d Not applicable (N/A). e Diethylamine (DEA). f 1,2-Diaminoethane (DAE). Effects of Markers on General Physical Properties of Marked Diesel Fuel. The study on the effects of petroleum markers on the general physical properties of marked diesel fuel was conducted in accordance with the ASTM methods, employing 3 ppm of 2-chloro-4- nitro-6-(4 -n-alkylphenylazo)-phenylamine (12) as a marker model. Stability of Petroleum Markers in Diesel Fuel. The quantity of each marker in diesel fuel was determined monthly for 3 months by the following procedure. The selected markers, 2-(4 -nitrophenylazo)-4-n-alkylphenylamine (1), 2-(2 -chloro-4 -nitrophenylazo)-4-nalkylphenylamine (5), 2-(2 -methoxy-4 -nitrophenylazo)- 4-n-alkylphenylamine (7), 4-nitro-2-(4 -n-alkylphenylazo)- phenylamine (8), 2-chloro-4-nitro-6-(4 -n-alkylphenylazo)- phenylamine (12), 2-methoxy-4-nitro-6-(4 -n-alkylphenylazo)-phenylamine (14), and 4-(4 -n-alkylphenylazo)- naphthalen-1-ol (19), were employed as models in this experiment; each (5 ppm) was dissolved in diesel fuel. The marked diesel fuels (30 ml) were separately pipetted into individual vials, and 5 ml of 50% (v/v) 1,2- diaminoethane in a solution containing propane-1,3-diol and methanol (2:3, v/v) was added to each. Each reaction vial was capped and shaken for 30 s. The VIS absorption (at λ max of the extraction system) of the lower phase was measured, and the determination of the quantity of petroleum marker in diesel fuel was performed by comparing the observed absorbance with the calibration curve. III. Results and Discussion Suitable Extraction System for the Detection of Petroleum Markers in Diesel Fuel. Petroleum markers 1-20 were successfully synthesized by coupling n-alkylaniline with aniline or phenol derivatives. All synthetic markers were either yellowish-brown or reddish-brown, which were regarded as appropriate colors that would not interfere with the intrinsic color of petroleum oils. To establish a suitable method for the detection of petroleum markers in diesel fuel, various extraction systems were designed and classified into two major types: acidic and basic conditions. The acidic systems were 10% (v/v) hydrochloric acid, 10% (v/v) formic acid, and 10% (v/v) acetic acid in propane-1,3-diol and methanol (2:3, v/v), while the basic systems were composed of 1-5% (w/v) potassium hydroxide, 10-50% (v/v) diethylamine, and 10-50% (v/v) 1,2-diaminoethane in a solution containing propane-1,3-diol and methanol (2:3, v/v). The marker 2-(4 -nitrophenylazo)-4-n-alkylphenylamine (1) was employed as a marker model. The VIS characteristics of the colors developed in acidic and basic extraction systems are reported in Table 1. It was found that extractions with acidic systems produced a dark yellow color in the extracted phase, whereas the basic extraction systems provided a red or purple color (Table 1). Thus, the basic extraction systems gave a color more easily distinguishable from the color of diesel fuel than did the acidic extraction systems. The shortest time required to separate the extracted phase from the oil phase was 6 min, whereas the longest time was 10 min (Table 1). The systems containing potassium hydroxide required a longer time (8-10 min) to separate than did the diethylamine and 1,2-diaminoethane systems. Furthermore, the color developed with potassium hydroxide solution was unstable, which critically hindered quantitative determinations. For the above reasons, the system with potassium hydroxide was not suitable for the extraction of markers from marked fuel. Although the system with diethylamine gave the maximum absorbance, generally higher than that obtained with the 1,2-diaminoethane system at a given concentration (Table 1), the diethylamine-containing system could be oxidized very easily within 24 h at room temperature. Consequently, the color of the extracted phase of the system with diethylamine changed, leading to error during the quantitative determinations of the markers. Therefore, the extraction system with diethylamine was not suitable for the detection of markers in dyed fuel. The extraction system containing 1,2-diaminoethane had an advantage in its stability (the color that developed in the extracted phase was found to be unchanged after 3 days at room temperature), and it also gave extract with a distinguishable color at a longer maxi-

5 5058 Ind. Eng. Chem. Res., Vol. 42, No. 21, 2003 Table 2. Percentage Yields from the Syntheses of Markers 1-20, VIS Absorbance at λ max, and Visual Colors a in the Extracted Phase When the B15 Extraction System Is Used marker yield (%) concentration (ppm) visual color λ max (nm) absorbance b purple ( yellow ( yellow ( yellow ( red ( yellow ( green ( purple ( yellow ( yellow ( yellow ( violet ( yellow ( green ( yellow ( yellow ( yellow ( yellow ( orange ( yellow ( a At a suitable concentration. b Average ( standard deviation, n ) 3. Table 3. VIS Absorbance of the Developed Colors When Using B15 Extraction System with Various Shaking Times a shaking time (s) visual color λ max (nm) absorbance b 10 purple ( purple ( purple ( purple ( purple ( a Dye 2-(4 -nitrophenylazo)-4-n-alkylphenylamine (1) in diesel fuel (10 ppm) was used as a marker model. b Average ( standard deviation, n ) 3. mum wavelength. It could therefore be concluded that the most suitable system for the extraction of markers from diesel fuel was the system with 1,2-diaminoethane. From Table 1, the maximum wavelength of developed color shifted to longer wavelength when the percentage of 1,2-diaminoethane was increased (systems B11-B15). This effect is commonly known as a bathochromic band shift or red shift. This bathochromic band shift presumably resulted from a reduction in the energy level of the excited state accompanying dipole-dipole interactions and hydrogen bonding between 1,2-diaminoethane and markers. Hence, 50% (v/v) 1,2-diaminoethane in a solution containing propane-1,3-diol and methanol (system B15 in Table 1) was the most suitable extraction system for the detection of markers in diesel fuel. The synthetic markers were added to diesel fuel and subsequently extracted with system B15, and the VIS absorbance at their maximum wavelengths and visual colors are reported in Table 2. It was found that each marker provided different distinctive colors in the extracted phase, and the selected extraction system can therefore be practically employed for qualitative determinations in a field test. Markers that showed clear distinguishable color in extraction system B15 were the dyes 1, 5, 7, 8, 12, 14, and 19 (Table 2). Considering the structures of these markers, one can see that these markers are substituted with a nitro or hydroxyl group at the para position. Although the complexation reaction of 1,2-diaminoethane and cosolvent with the markers is not fully understood, the following mechanism possibly occurs: First, the complexation reaction results in the oil-soluble marker being rendered soluble in aqueous medium and thereby extractable into an aqueous phase. Then, the reaction undergoes color development in an aqueous phase. Optimum Shaking Time for the Detection of Petroleum Markers in Diesel Fuel. The optimum shaking time for the detection of marker in diesel fuel was studied, employing 2-(4 -nitrophenylazo)-4-n-alkylphenylamine (1) (10 ppm) as a marker model (Table 3). It was found that the absorbance increased proportionally to the shaking time from 10 to 30 s and remained constant from 30 to 50 s. Thus, the shaking time of 30 s was deemed suitable for the extraction of markers from diesel fuel to an extracted phase and was consequently employed throughout this research. Efficiency of Extraction Systems. The efficiency of each extraction system was studied using 2-(4 -nitrophenylazo)-4-n-alkylphenylamine (1) as a marker model. The VIS absorption of the extracted phase was This VIS absorption was compared to the calibration curve, from which the equation Y ) ( )X - ( ) was derived. The calibration curve readily indicated a dye concentration of ppm, so Table 4. General Physical Properties of Marked a and Unmarked Diesel Fuels method diesel fuel c physical property (ASTM b ) unmarked marked API gravity at 15.6 C D ( ( 0.0 specific gravity at 15.6/15.6 C D ( ( 0.0 calculated cetane index D ( ( 0.0 kinematic viscosity at 40 C (cst) D ( ( pour point ( C) D ( ( 0.0 flash point ( C) D ( ( sulfur content (% w/w) D ( ( 0.0 copper strip corrosion (3 h, 50 C) D-130 no. 1 no. 1 distillation D-86 IBP d ( C) ( ( % recovery ( C) ( ( % recovery ( C) ( ( % recovery ( C) ( ( total acid number (mg of KOH/g) D ( ( color D-1500 <0.5 <0.5 a Diesel fuel was marked with 2-chloro-4-nitro-6-(4 -n-alkylphenylazo)-phenylamine (12) (3 ppm). b American Society for Testing and Materials (ASTM). c Average ( standard deviation, n ) 2. d Initial boiling point (IBP).

6 Ind. Eng. Chem. Res., Vol. 42, No. 21, Table 5. Concentrations of 2-(4 -Nitrophenylazo)- 4-n-alkylphenylamine (1) (5 ppm), 2-(2 -Chloro- 4 -nitrophenylazo)-4-n-alkylphenylamine (5) (4 ppm), 2-(2 -Methoxy-4 -nitrophenylazo)-4-n-alkylphenylamine (7) (5 ppm), 4-Nitro-2-(4 -n-alkylphenylazo)-phenylamine (8) (5 ppm), 2-Chloro-4-nitro-6-(4 -n-alkylphenylazo)- phenylamine (12) (3 ppm), 2-Methoxy-4-nitro- 6-(4 -n-alkylphenylazo)-phenylamine (14) (5 ppm), and 4-(4 -n-alkylphenylazo)-naphthalen-1-ol (19) (3 ppm) in Diesel Fuel over a Period of 3 Months concentration a (ppm) marker month 1 month 2 month ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( 0.02 a Average ( standard deviation, n ) 3. 5 ml of extracted phase should contain mg of marker 1, which accounted for 97.92% (w/w) when compared with the dye content in the original marked diesel fuel. Replicate experiments were performed and gave the percent of extraction (average ( standard deviations) of ( 0.22% (w/w), when using 50% (v/v) 1,2-diaminoethane in a solution containing propane-1,3-diol and methanol (2:3, v/v) as the extraction system. Effects of Markers on General Physical Properties of Marked Diesel Fuel. Physical properties of the marked and unmarked diesel fuel (with marker 12) are listed in Table 4. The physical properties of the marked diesel fuel were not significantly different from those of the unmarked diesel fuel. Both marked and unmarked diesel fuels provided similar specific gravities, calculated cetane indexes, kinematic viscosities, pour points, flash points, distillation properties, and colors. Marker model 12 did not exhibit any effects on the physical properties of the diesel fuel (Table 4); it is therefore possible to assume that the series of synthetic markers 1-20 would not alter any physical properties of the fuel oil. Stability of Petroleum Markers in Diesel Fuel. The stability of markers in diesel fuel was studied employing 2-(4 -nitrophenylazo)-4-n-alkylphenylamine (1), 2-(2 -chloro-4 -nitrophenylazo)-4-n-alkylphenylamine (5), 2-(2 -methoxy-4 -nitrophenylazo)-4-n-alkylphenylamine (7), 4-nitro-2-(4 -n-alkylphenylazo)-phenylamine (8), 2-chloro-4-nitro-6-(4 -n-alkylphenylazo)-phenylamine (12), 2-methoxy-4-nitro-6-(4 -n-alkylphenylazo)-phenylamine (14), and 4-(4 -n-alkylphenylazo)-naphthalen-1- ol (19) as marker models (Table 5). There were no significant changes in the concentrations of the markers in diesel fuel throughout the period of 3 months (Table 5). Generally, each batch of fuel oil is consumed within 3 months after release to the market; it is therefore possible that these markers could be readily applied as petroleum markers in commercial fuel oils. IV. Conclusions Potential fuel markers 1-20 were synthesized using two methods. The first method was a coupling reaction of n-alkylaniline (which was obtained from nitration and reduction reactions of n-alkylbenzene) with a diazonium salt of seven aniline derivatives, including 4-nitroaniline, 2-nitroaniline, 4-chloro-2-nitroaniline, 4-chloro- 3-nitroaniline, 2-chloro-4-nitroaniline, 2-chloro-5-nitroaniline, and 2-methoxy-4-nitroaniline. The second method was a coupling reaction of a diazonium salt of n- alkylaniline with the above aniline derivatives or six phenol derivatives, including phenol, benzene-1,3-diol, benzene-1,2-diol, 2,6-di-tert-butylphenol, naphthalen-1- ol, and naphthalen-2-ol. These markers were invisible in diesel fuel at an effectively usable level, but they provided distinctive colors in the extracted phase following extraction with 50% (v/v) 1,2-diaminoethane in a solution containing propane-1,3-diol and methanol (2:3, v/v). As revealed by tests performed according to ASTM methods, these markers did not alter the physical properties of the diesel fuel. Furthermore, these markers were found to be stable in diesel fuel over a period of at least 3 months. Acknowledgment The RGJ-Ph.D. scholarship to S.S. is gratefully acknowledged. We are grateful to the Petroleum Authority of Thailand for testing the physical properties of the marked and unmarked diesel fuels. We thank Dr. P. Kittakoop for his comments and suggestions on the manuscript. Supporting Information Available: Spectral data (FT-IR, ESITOF MS, 1 H and 13 C NMR) of markers This material is available free of charge via the Internet at Literature Cited (1) Orelup, R. B. Method for Detecting a Tagging Compound. U.S. Patent 4,764,474, 1988; Chem. Abstr. 1988, 103, (2) Smith, M. J.; Desai B. Colorless Petroleum Markers. U.S. Patent 6,002,056, 1999; Chem. Abstr. 1999, 126, 9890t. (3) Friswell, M. R.; Hinton, M. P. 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Method for Tagging Petroleum Products. U.S. Patent 5,525,516, 1996; Chem. Abstr. 1996, 125, 37859n. (11) Adam, R.; Johnson, J. R.; Wilcox, C. F. Laboratory Experiments in Organic Chemistry; Macmillan: New York, 1970; p 295. (12) Smith, M. J.; Desai, B.; Frederico, J. J. Molecular Tags for Organic Solvent Systems. U.S. Patent 6,514,917 B1, 2003; Chem. Abstr. 1996, 138, Received for review June 24, 2002 Revised manuscript received June 12, 2003 Accepted June 15, 2003 IE020472H