1、Designation: D 4936 05Standard Test Method forMercaptobenzothiazole Sulfenamide Assay by Reduction/Titration1This standard is issued under the fixed designation D 4936; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of assay onmercaptobenzothiazole (MBT) sulfenamides. It is based on atitratio
3、n of the basic amines liberated upon reduction of thesulfenamides with hydrogen sulfide gas (H2S)2,3or2-mercaptobenzothiazole.1.2 Any free amine (HNR2) or weak acid salts of thecorresponding amine (HXHNR2) are titrated prior to reduc-tion. This titer is used to calculate percent basic impurity (asfr
4、ee amine) in the sample.1.3 With the indicated modifications, this test method isapplicable to all MBT sulfenamides, that is, N-cyclohexyl-2-benzothiazolesulfenamide (CBS), N,N-diisopropyl-2-benzothiazyl sulfenamide (DIBS), 2 (morpholinothio) ben-zothiazole (MBS), N,N-dicylohexyl-2-benzothiazylsulfe
5、namide (DCBS), N-tert-butyl-benzothiazole-sulfenamide(TBBS), and 4-morpholinyl-2-benzothiazyl disulfide (MBSS).1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.5 This standard does not purport to address all of thesafety c
6、oncerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements, see Section 9.2. Referenced Documents2.1 ASTM S
7、tandards:4D 4483 Practice for Determining Precision for Test MethodStandards in the Rubber and Carbon Black Industries3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 IpOH/Tol solvent, ntitration solvent containing fivevolumes isopropanol and three volumes toluene.3.1.2 “lot” s
8、ample, na production sample representativeof a standard production unit.3.1.3 potassium hydrogen phthalate acidimetric standard,nFisher P-243.53.1.4 primary titrant, n0.25 to 0.30 N aqueous hydrochlo-ric acid (HCl).3.1.5 reducing solution, nIpOH/Tol solvent saturated withhydrogen sulfide gas (H2S) a
9、t 25C (about 1.1 g H2S/100 mLsolvent).3.1.6 test unit, nthe actual material used in the analysis. Itmust be representative of the “lot” sample.3.2 Abbreviations:3.2.1 THAMtris (hydroxymethyl) aminomethane alkali-metric standard (Fisher T-395).34. Summary of Test Method4.1 Procedure AFor CBS, TBBS, M
10、BSS, MBS-90, andMBS, a weighed specimen is dissolved in the appropriatesolvent, the “free amine” blank is titrated with standard acid,and the sulfenamide is reduced with H2S. That is,BtSNR21 H2SBtSH 1 HNR21 S (1)where:Bt = the 2-benzothiazole radical.BtSH = 2-mercaptobenzothiazole.HNR2= free amine.T
11、he liberated amine is then titrated with standard acid to anindicator end point.1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.11 on Chemical Analysis.Current edition approved Oct. 1, 2005. Published November 2005. Orig
12、inallyapproved in 1989. Last previous edition approved in 2001 as D 493696(2001).2Goodyear Paper, Industrial and Engineering Chemistry Production Researchand Development, Vol 2, 1963, p. 16.3Elastomerics, August 1981, pp. 3444.4For referenced ASTM standards, visit the ASTM website, www.astm.org, orc
13、ontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.5The sole source of supply of the apparatus known to the committee at this timeis Fisher Scientific Co., 711 Forbes Ave., Pittsburgh,
14、PA 15219. If you are aware ofalternative suppliers, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.1Copyright ASTM International, 100 Barr Harbor Drive, PO Bo
15、x C700, West Conshohocken, PA 19428-2959, United States.4.2 Procedure BFor sulfenamides of hindered amines(DIBS and DCBS), it is necessary to measure the liberatedamine by back titration at 40 to 45C. Excess hydrochloric acid(HCl) is added, then back titrated with standard sodiumhydroxide (NaOH).4.3
16、 Procedure CThis alternative is appropriate for allsulfenamides. A weighed specimen is dissolved in ethanol, the“free amine” blank is titrated with standard acid, and thesulfenamide reduced with MBT. That is,BtSNR21 BtSHBtSSBt 1 HNR2(2)where:BtSSBt = benzothiazole disulfide.The liberated amine is ca
17、ptured in a known amount ofstandard acid and the excess acid back titrated with standardsodium hydroxide.5. Significance and Use5.1 This test method is designed to assess the purity of2-mercaptobenzothiazole sulfenamide accelerators. Theseproducts are used in combination with sulfur for the vulcani-
18、zation of rubber.5.2 The test method is suitable for assessing product speci-fications in that the property it measures is related to productperformance. Since it is the primary property for comparison ofproduct quality at different production facilities, good inter-laboratory accuracy and precision
19、 is required.5.3 Based on past experience, two significant sources oferror in this test method are: (1) incomplete reduction and (2)titration end point assessment. Problems in these areas can beavoided by closely following the procedure.6. Interferences6.1 Theoretically, any material that is reduced
20、 to an acidtitratable entity will be measured by this test method. Extensivehigh-pressure liquid chromatograph (HPLC) analysis of sulfe-namides indicates that the most significant interfering impurityis the corresponding sulfinamide, BtSONR2.6.2 The corresponding sulfonamide, BtSO2NR2, is presentin
21、some samples, but it does not reduce under the analyticalconditions.7. Apparatus7.1 Standard Laboratory Glassware and Equipment.7.2 Buret, 10-cm3, Class A, graduated in 0.05-cm3incre-ments.7.3 Buret,25cm3, Class A, graduated in 0.05 cm3incre-ments.7.4 Buret, 50-cm3, Class A, graduated in 0.10-cm3inc
22、re-ments.7.5 Pipet,2cm3, Class A, graduated in 0.1 cm3increments.7.6 Pipet,25cm3, Class A.7.7 Hydrogen Sulfide Lecture Sphere (99.5 % purity),5ispreferred for convenience, ease, and correctness of saturatedsolution preparation. Lecture bottles or larger H2S containersare acceptable, but means should
23、 be developed to establishamount used in preparing a saturated solution.7.8 H2S Trap Train,1dm3NaOH (12 %) followed by 1 dm3NaOH (25 %) followed bya1dm3water trap (see Fig. 1).7.9 Platform Balance, 8000 g, for weighing the H2S cylin-der to the nearest 1 g.7.10 Magnetic Stirrer.7.11 Gas Dispersion Tu
24、be,123 250 mm stem, 40-60 mpore size; 12C.7.12 Gas Valve, for H2S cylinder, stainless steel, GCA 110inlet (fits lecture sphere on lecture bottles).7.13 pH Meter with a sensitivity of 0.1 pH unit with a glassmeasuring electrode and a calomel reference electrode.7.14 Bath, thermostatically controlled.
25、7.15 High Precision Balance, for weighing specimen tonearest 0.1 mg.8. Reagents8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Che
26、mical Society wheresuch specifications are available.6Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.8.2 Bromophenol Blue Indicator SolutionBromophenolblue (BPB) in isopropa
27、nol, 1 % mass/volume (ProcedureAandB). Bromophenol blue (BPB) in ethanol, 1 % weight/volume(Procedure C).8.3 Hydrochloric Acid (0.25 to 0.30 N)Aqueous hydro-chloric acid (HCl) titrant, prepared in an acid carboy (2 dm3ormore).8.4 Hydrochloric Acid (0.1 N)Aqueous HCl titrant.8.5 Hydrochloric Acid (0.
28、5 N)Aqueous HCl (ProceduresB and C).8.6 Isopropanol-Toluene Solvent (IpOH/Tol)Mix five vol-umes reagent grade isopropanol with three volumes reagentgrade toluene.6Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of
29、reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.FIG. 1 H2S Saturation AssemblyD49360528.7 Phenolphthale
30、in Indicator SolutionPhenolphthaleinin isopropanol, 1 % mass/volume.8.8 Potassium Hydrogen Phthalate Acidimetric StandardFisher P-2433(Procedure B). Store in a desiccator at roomtemperature.8.9 Reducing SolutionIpOH/Tol solvent saturated withH2S at room temperature (see 12.1 for saturation procedure
31、).8.10 Sodium Hydroxide (0.25 to 0.3 N)Aqueous sodiumhydroxide (NaOH) (Procedure B).8.11 Aqueous NaOH (0.5 N)Procedure C.8.12 THAM Alkalimetric StandardFisher T-395.3(Storein desiccator at room temperature.)8.13 Absolute ethanol.8.14 2-mercaptobenzothiazole (MBT), min 99 %Weigh 4g MBT to the nearest
32、 0.1 g in a 100 cm3volumetric flask,dissolve in absolute ethanol with warming and dilute to volumewith absolute ethanol.8.14.1 Prepare sufficient volume of reagent for the numberof tests anticipated at the time.9. Hazards9.1 Hydrogen sulfide is a toxic gas and should only behandled in a laboratory h
33、ood. (The American Conference ofGovernment Industrial Hygienists gives 14 mg/m3as the timeweighted average-threshold limit values (TWA-TLVs) and 21mg/m3as the short-term exposure limit (STEL).7)9.2 The prescribed traps should be used for “catching”unused H2S when preparing the reagent. Also, all sol
34、utions(after completion of test) should be quenched with 10 % NaOHand discarded in a container maintained in the hood. Theglassware should then be rinsed with additional caustic solu-tion before being removed from the hood.9.3 Toluene and isopropanol, with TLVs of 200 mg/kg(ppm) and 400 mg/kg (ppm),
35、 respectively, and high flamma-bility, should be handled with appropriate precaution.9.4 Good laboratory safety practices should be followed inhandling all chemicals and carrying out manipulations.10. Sampling10.1 To ensure sample homogeneity, a minimum of 10 g ofa “lot” sample should be ground with
36、 a mortar and pestle. (Thisis not necessary for analytical standards.) The test unit (2 g)should be taken from this composite.11. Calibration and Standardization11.1 As is the case with any titration method, it is extremelyimportant that the titrants be accurately standardized. Theorganic base THAM
37、is used as the primary standard since it issoluble in the isopropanol-toluene solvent and has an equiva-lence point at essentially the same pH as the amines beingtitrated (see Appendix X1).11.2 The primary titrant (0.25 to 0.30 N HCl) is prepared bydiluting concentrated HCl (12 N) 44 to 1 with water
38、. To prepare2dm3, add 45 cm3concentrated HCl to a 2-dm3containerpartially filled with deionized water and dilute to volume withadditional water. Mix thoroughly before standardization.11.3 Weigh 1.3 to 1.5 g THAM to the nearest 0.1 mg in a250-cm3Erlenmayer flask, dissolve in 10 cm3of water, andadd 15
39、0 cm3IpOH/Tol solution. Add five drops of indicatorand titrate with the primary titrant to the “first” yellow (pH 4).This is the point where the green hue is approaching yellow(see Fig. 2).11.4 An illustration of the color changes, as a function of pHnear the end point, is presented inAppendix X1. T
40、his should becarefully reviewed with each individual carrying out the test.11.5 Also note that the rate of titrant addition should beslowed progressively as the end point is approached. When theblue-green is initially detected (pH 5), the addition incrementsshould be no more than about 0.1 cm3(two d
41、rops).11.6 The normality, N, of the primary titrant is calculated asfollows:N 5TVHCl! 0.12114!(3)where:T = mass of THAM, g,VHCl= volume of HCl, cm3, and0.12114 = equivalent mass of THAM divided by 1000.The titrant normality, N, should be assigned as the average ofat least three replicates that check
42、 within 0.0004 N. (Runadditional standards for those outside this range.)11.7 The secondary titrant (0.1 N HCl) should be standard-ized in a similar manner but using only 0.1 to 0.2 g THAM.Although care is needed in standardizing this solution, it ismuch less critical than the primary titrant. (It i
43、s also acceptableto prepare the secondary titrant by quantitative dilution of theprimary titrant, thus saving standardization time.)11.8 When using Procedure B, it is necessary to prepare andstandardize aqueous NaOH (0.3 N) and aqueous HCl (0.5 N)solutions.11.8.1 Dissolve 12 g NaOH pellets in 1 dm3o
44、f water toprepare 0.3 N NaOH. To standardize, weigh, to nearest 1 mg,about 2.3 g of potassium hydrogen phthalate, dissolve in 100cm3water, add three drops phenolphthalein indicator, andtitrate with NaOH to phenolphthalein end point.7American Conference of Government Industrial Hygienists, 1980. FIG.
45、 2 Titration of 1.3755 g THAMD493605311.8.2 Prepare 0.5 N HCl by diluting concentrated HCl (12N) 25 to 1 with water. Standardize as in 11.3.11.8.3 When using Procedure C, it is necessary to prepareand standardize aqueous NaOH (0.5 N) in addition to the HCl(0.1 N and 0.5 N) described in 11.7 and 11.8
46、.2 respectively.Dissolve 20 g NaOH pellets in 1 dm3water and standardize asin 11.8.1.12. Procedure12.1 Preparation of Reducing SolutionJust prior to use,prepare enough solution to analyze the number of samplesanticipated by the following procedure. Set up the apparatusshown in Fig. 1 in a high draft
47、 hood. Sparge 15 g of H2S perlitre of IpOH/Tol solvent at a rate of approximately 0.5 g/minat room temperature. Stir the solution continuously untilsaturation is achieved. This condition is indicated by anincrease in bubble rate and size in the solvent as well as greater“activity” in the first caust
48、ic trap. The measured solubility ofH2S in IpOH/Tol is 1.08 g/100 cm3at 25C. If the H2Sisfedby weight (or volume) and this solubility factor is kept in mind,complete saturation will always be achieved. (Incompletesaturation is a major cause of bad results by this test method.)12.2 Store the reducing
49、solution loosely capped at a tem-perature 25C. In the event that it will not be used immediately,cool to 5C below saturation temperature by storing in a waterbath. At the conclusion of the analysis set, discard unusedsolution by quenching in 10 % caustic. (Although it may beacceptable to resaturate solution and use later, it becomesdifficult to be assured that saturation is achieved.)12.3 Procedure AThis procedure is for CBS, TBBS,MBSS, and MBS.12.3.1 Prepare the sample according to 10.1 and weigh thetest unit (2.0 g to nearest 0.1 mg) into a 250-c
