1、Designation: D4936 10Standard Test Method forMercaptobenzothiazole Sulfenamide Assay by Reduction/Titration1This standard is issued under the fixed designation D4936; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 atitration o
3、f 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 (asfree
4、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-benzothiazylsulfenam
5、ide (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 conc
6、erns, 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 Stan
7、dards:4D4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustries3. 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
8、 “lot” sample, 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
9、 (H2S) at 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,
10、 TBBS, MBSS, 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
11、 amine.The liberated amine is then titrated with standard acid to anindicator end point.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 sta
12、ndard sodiumhydroxide (NaOH).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 Dec. 1, 2010. Published January 2011. Originallyapproved in 1989. Last previous edition approv
13、ed in 2005 as D4936 05. DOI:10.1520/D4936-10.2Goodyear 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, orcontact ASTM Customer Service at serv
14、iceastm.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, PA 15219. If you are aware ofalterna
15、tive 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 Box C700, West Conshohocken, PA 19428-
16、2959, United States.4.3 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.Th
17、e liberated amine is captured 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
18、sulfur for the vulcani-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
19、 accuracy and precision 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 m
20、aterial that is reduced 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,
21、BtSO2NR2, is presentin 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, g
22、raduated in 0.10-cm3incre-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 accep
23、table, but means should 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
24、.7.11 Gas Dispersion Tube,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, therm
25、ostatically controlled.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 Reage
26、nts of the American Chemical 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 SolutionBromopheno
27、lblue (BPB) in isopropanol, 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.
28、5 Hydrochloric Acid (0.5 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.8.7 Phenolphthalein Indicator SolutionPhenolphthaleinin isopropanol, 1 % mass/volume.8.8 Potassium Hydrogen Phthala
29、te Acidimetric StandardFisher P-2433(Procedure B). Store in a desiccator at roomtemperature.6Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Stand
30、ards 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 AssemblyD4936 1028.9 Reducing SolutionIpOH/Tol solvent saturated withH2S at room temperature (see 12.1
31、 for saturation procedure).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 %We
32、igh 4g MBT to the nearest 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 be
33、handled in a laboratory hood. (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 t
34、he reagent. Also, all solutions(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(
35、ppm) and 400 mg/kg (ppm), 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” sam
36、ple should be ground with 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 standardiz
37、ed. Theorganic base THAM 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
38、(12 N) 44 to 1 with water. 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
39、10 cm3of water, andadd 150 cm3IpOH/Tol solution. Add five drops of indicatorand titrate with the primary titrant to the green (pH 4). This isthe 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
40、inAppendix X1. This 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 abo
41、ut 0.1 cm3(two drops).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 repli
42、cates that check 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 primar
43、y titrant. (It is 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 p
44、ellets in 1 dm3of 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.11.8.2 Prepare 0.5 N HCl by diluting concentrated HC
45、l (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 11.8.2 respectively.Dissolve 20 g NaOH pellets in 1 dm3water and standardize asin 11.8.1.7Ame
46、rican Conference of Government Industrial Hygienists, 1980.FIG. 2 Titration of 1.3755 g THAMD4936 10312. 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
47、 in a high draft 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
48、 the first caustic 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 Sto
49、re the reducing 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
