2-Propanethiol, 2-methyl-
- Formula: C4H10S
- Molecular weight: 90.187
- IUPAC Standard InChIKey: WMXCDAVJEZZYLT-UHFFFAOYSA-N
- CAS Registry Number: 75-66-1
- Chemical structure:
This structure is also available as a 2d Mol file or as a computed 3d SD file
The 3d structure may be viewed using Java or Javascript. - Other names: tert-Butanethiol; tert-Butylmercaptan; tert-Butylthiol; 1,1-Dimethylethanethiol; 2-Isobutanethiol; 2-Methyl-2-propanethiol; tert-C4H9SH; t-Butyl mercaptan; tert-Butyl hydrosulfide; 2-Methyl-2-propylthiol; tertiary-Butyl mercaptan; 2-methylpropane-2-thiol
- Permanent link for this species. Use this link for bookmarking this species for future reference.
- Information on this page:
- Other data available:
- Data at other public NIST sites:
- Options:
Data at NIST subscription sites:
NIST subscription sites provide data under the NIST Standard Reference Data Program, but require an annual fee to access. The purpose of the fee is to recover costs associated with the development of data collections included in such sites. Your institution may already be a subscriber. Follow the links above to find out more about the data in these sites and their terms of usage.
Gas phase thermochemistry data
Go To: Top, Condensed phase thermochemistry data, Phase change data, Reaction thermochemistry data, Gas Chromatography, References, Notes
Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.
Data compiled by: Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
Quantity | Value | Units | Method | Reference | Comment |
---|---|---|---|---|---|
ΔfH°gas | -25.99 ± 0.21 | kcal/mol | Ccr | Hubbard, Good, et al., 1958 | see Hubbard, Katz, et al., 1954 and McCullough, Scott, et al., 1953 |
Condensed phase thermochemistry data
Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Gas Chromatography, References, Notes
Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.
Data compiled as indicated in comments:
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
DH - Eugene S. Domalski and Elizabeth D. Hearing
Quantity | Value | Units | Method | Reference | Comment |
---|---|---|---|---|---|
ΔfH°liquid | -33.59 ± 0.21 | kcal/mol | Ccr | Hubbard, Good, et al., 1958 | Reanalyzed by Cox and Pilcher, 1970, Original value = -33.38 ± 0.20 kcal/mol; see Hubbard, Katz, et al., 1954 and McCullough, Scott, et al., 1953; ALS |
Quantity | Value | Units | Method | Reference | Comment |
ΔcH°liquid | -828.15 ± 0.17 | kcal/mol | Ccr | Hubbard, Good, et al., 1958 | Reanalyzed by Cox and Pilcher, 1970, Original value = -828.00 ± 0.17 kcal/mol; see Hubbard, Katz, et al., 1954 and McCullough, Scott, et al., 1953; ALS |
Quantity | Value | Units | Method | Reference | Comment |
S°liquid | 58.901 | cal/mol*K | N/A | McCullough, Scott, et al., 1953, 2 | DH |
Constant pressure heat capacity of liquid
Cp,liquid (cal/mol*K) | Temperature (K) | Reference | Comment |
---|---|---|---|
41.840 | 298.15 | McCullough, Scott, et al., 1953, 2 | T = 12 to 329 K.; DH |
Phase change data
Go To: Top, Gas phase thermochemistry data, Condensed phase thermochemistry data, Reaction thermochemistry data, Gas Chromatography, References, Notes
Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.
Data compiled as indicated in comments:
BS - Robert L. Brown and Stephen E. Stein
TRC - Thermodynamics Research Center, NIST Boulder Laboratories, Chris Muzny director
AC - William E. Acree, Jr., James S. Chickos
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
DRB - Donald R. Burgess, Jr.
CAL - James S. Chickos, William E. Acree, Jr., Joel F. Liebman, Students of Chem 202 (Introduction to the Literature of Chemistry), University of Missouri -- St. Louis
DH - Eugene S. Domalski and Elizabeth D. Hearing
Quantity | Value | Units | Method | Reference | Comment |
---|---|---|---|---|---|
Tboil | 337. ± 2. | K | AVG | N/A | Average of 8 values; Individual data points |
Quantity | Value | Units | Method | Reference | Comment |
Tfus | 273.97 | K | N/A | Denyer, Fidler, et al., 1949 | Uncertainty assigned by TRC = 0.2 K; TRC |
Quantity | Value | Units | Method | Reference | Comment |
Ttriple | 274.42 | K | N/A | McCullough, Scott, et al., 1953, 3 | Crystal phase 1 phase; Uncertainty assigned by TRC = 0.02 K; TRC |
Quantity | Value | Units | Method | Reference | Comment |
Tc | 530.1 | K | N/A | Majer and Svoboda, 1985 | |
Quantity | Value | Units | Method | Reference | Comment |
ΔvapH° | 7.392 | kcal/mol | N/A | Majer and Svoboda, 1985 | |
ΔvapH° | 7.36 | kcal/mol | N/A | Reid, 1972 | AC |
ΔvapH° | 7.39 ± 0.02 | kcal/mol | E | Hubbard, Good, et al., 1958 | see Hubbard, Katz, et al., 1954 and McCullough, Scott, et al., 1953; ALS |
ΔvapH° | 7.60 | kcal/mol | N/A | Hubbard, Good, et al., 1958 | DRB |
Enthalpy of vaporization
ΔvapH (kcal/mol) | Temperature (K) | Method | Reference | Comment |
---|---|---|---|---|
6.800 | 337.4 | N/A | Majer and Svoboda, 1985 | |
7.19 | 284. | N/A | Stockton, Ng, et al., 1998 | Based on data from 275. to 293. K.; AC |
7.39 | 308. | A,EB | Stephenson and Malanowski, 1987 | Based on data from 293. to 373. K. See also McCullough, Scott, et al., 1953, 2 and Osborn and Douslin, 1966.; AC |
Enthalpy of vaporization
ΔvapH =
A exp(-βTr) (1 − Tr)β
ΔvapH =
Enthalpy of vaporization (at saturation pressure)
(kcal/mol)
Tr = reduced temperature (T / Tc)
View plot Requires a JavaScript / HTML 5 canvas capable browser.
Temperature (K) | A (kcal/mol) | β | Tc (K) | Reference | Comment |
---|---|---|---|---|---|
298. to 337. | 11.23 | 0.3044 | 530.1 | Majer and Svoboda, 1985 |
Antoine Equation Parameters
log10(P) = A − (B / (T + C))
P = vapor pressure (atm)
T = temperature (K)
View plot Requires a JavaScript / HTML 5 canvas capable browser.
Temperature (K) | A | B | C | Reference | Comment |
---|---|---|---|---|---|
293.7 to 372.29 | 3.90701 | 1115.572 | -51.835 | McCullough, Scott, et al., 1953, 2 | Coefficents calculated by NIST from author's data. |
Enthalpy of fusion
ΔfusH (kcal/mol) | Temperature (K) | Reference | Comment |
---|---|---|---|
0.593 | 274.4 | Domalski and Hearing, 1996 | AC |
Entropy of fusion
ΔfusS (cal/mol*K) | Temperature (K) | Reference | Comment |
---|---|---|---|
6.413 | 151.6 | Domalski and Hearing, 1996 | CAL |
0.987 | 157. | ||
1.16 | 199.4 | ||
2.16 | 274.4 |
Enthalpy of phase transition
ΔHtrs (kcal/mol) | Temperature (K) | Initial Phase | Final Phase | Reference | Comment |
---|---|---|---|---|---|
0.97199 | 151.6 | crystaline, IV | crystaline, III | McCullough, Scott, et al., 1953, 2 | DH |
0.1549 | 157.0 | crystaline, III | crystaline, II | McCullough, Scott, et al., 1953, 2 | DH |
0.2320 | 199.4 | crystaline, II | crystaline, I | McCullough, Scott, et al., 1953, 2 | DH |
0.59319 | 274.42 | crystaline, I | liquid | McCullough, Scott, et al., 1953, 2 | DH |
Entropy of phase transition
ΔStrs (cal/mol*K) | Temperature (K) | Initial Phase | Final Phase | Reference | Comment |
---|---|---|---|---|---|
6.413 | 151.6 | crystaline, IV | crystaline, III | McCullough, Scott, et al., 1953, 2 | DH |
0.987 | 157.0 | crystaline, III | crystaline, II | McCullough, Scott, et al., 1953, 2 | DH |
1.16 | 199.4 | crystaline, II | crystaline, I | McCullough, Scott, et al., 1953, 2 | DH |
2.16 | 274.42 | crystaline, I | liquid | McCullough, Scott, et al., 1953, 2 | DH |
Reaction thermochemistry data
Go To: Top, Gas phase thermochemistry data, Condensed phase thermochemistry data, Phase change data, Gas Chromatography, References, Notes
Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.
Data compiled as indicated in comments:
B - John E. Bartmess
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
Note: Please consider using the reaction search for this species. This page allows searching of all reactions involving this species. A general reaction search form is also available. Future versions of this site may rely on reaction search pages in place of the enumerated reaction displays seen below.
Individual Reactions
C4H9S- + =
By formula: C4H9S- + H+ = C4H10S
Quantity | Value | Units | Method | Reference | Comment |
---|---|---|---|---|---|
ΔrH° | 352.5 ± 2.2 | kcal/mol | G+TS | Bartmess, Scott, et al., 1979 | gas phase; value altered from reference due to change in acidity scale; B |
Quantity | Value | Units | Method | Reference | Comment |
ΔrG° | 346.2 ± 2.0 | kcal/mol | IMRE | Bartmess, Scott, et al., 1979 | gas phase; value altered from reference due to change in acidity scale; B |
By formula: H2O + C6H12OS = C2H4O2 + C4H10S
Quantity | Value | Units | Method | Reference | Comment |
---|---|---|---|---|---|
ΔrH° | -3.00 ± 0.07 | kcal/mol | Cm | Wadso, 1957 | liquid phase; Heat of hydrolysis; ALS |
Gas Chromatography
Go To: Top, Gas phase thermochemistry data, Condensed phase thermochemistry data, Phase change data, Reaction thermochemistry data, References, Notes
Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.
Data compiled by: NIST Mass Spectrometry Data Center, William E. Wallace, director
Kovats' RI, non-polar column, isothermal
Column type | Active phase | Temperature (C) | I | Reference | Comment |
---|---|---|---|---|---|
Capillary | DB-5 | 100. | 605.5 | Miller and Bruno, 2003 | 30. m/0.25 mm/0.1 μm |
Capillary | DB-5 | 120. | 617.0 | Miller and Bruno, 2003 | 30. m/0.25 mm/0.1 μm |
Capillary | DB-5 | 60. | 599.2 | Miller and Bruno, 2003 | 30. m/0.25 mm/0.1 μm |
Capillary | DB-5 | 80. | 602.5 | Miller and Bruno, 2003 | 30. m/0.25 mm/0.1 μm |
Packed | Apiezon M | 130. | 602. | Garbuzov, Misharina, et al., 1985 | He or N2, Chromosorb W, AW-DMCS; Column length: 2.1 m |
Packed | Apiezon M | 60. | 586. | Mikhailova, Gren, et al., 1985 | Chromosorb WAW; Column length: 2.1 m |
Packed | Squalane | 60. | 574. | Zygmunt and Staszewski, 1981 | Chromosorb W DMCS; Column length: 2. m |
Packed | Squalane | 80. | 577. | Zygmunt and Staszewski, 1981 | Chromosorb W DMCS; Column length: 2. m |
Packed | Apiezon M | 130. | 603. | Golovnya and Garbuzov, 1974 | N2, Chromosorb W; Column length: 2.1 m |
Kovats' RI, non-polar column, custom temperature program
Column type | Active phase | I | Reference | Comment |
---|---|---|---|---|
Capillary | Apiezon M | 602. | Zhu, Wang, et al., 2007 | Program: not specified |
Kovats' RI, polar column, custom temperature program
Column type | Active phase | I | Reference | Comment |
---|---|---|---|---|
Capillary | PEG-20M | 779. | Zhu, Wang, et al., 2007 | Program: not specified |
Normal alkane RI, non-polar column, isothermal
Column type | Active phase | Temperature (C) | I | Reference | Comment |
---|---|---|---|---|---|
Capillary | Polydimethyl siloxane with 5 % Ph groups | 100. | 606. | Safa and Hadjmohannadi, 2005 | 30. m/0.25 mm/0.10 μm, Nitrogen |
Capillary | Polydimethyl siloxane with 5 % Ph groups | 60. | 599. | Safa and Hadjmohannadi, 2005 | 30. m/0.25 mm/0.10 μm, Nitrogen |
Capillary | Polydimethyl siloxane with 5 % Ph groups | 80. | 602. | Safa and Hadjmohannadi, 2005 | 30. m/0.25 mm/0.10 μm, Nitrogen |
Normal alkane RI, non-polar column, temperature ramp
Column type | Active phase | I | Reference | Comment |
---|---|---|---|---|
Capillary | PONA | 584. | Yang, Wang, et al., 2004 | 50. m/0.20 mm/0.50 μm, N2, 2. K/min; Tstart: 35. C; Tend: 170. C |
Capillary | PONA | 594. | Yang, Wang, et al., 2003 | 50. m/0.20 mm/0.50 μm, 2. K/min; Tstart: 30. C; Tend: 150. C |
Packed | Porapack Q | 600. | Guevas A.P. and Tellez, 1977 | Helium, Porapak Q, 8. K/min; Column length: 3.5 m; Tstart: 220. C |
Normal alkane RI, non-polar column, custom temperature program
Column type | Active phase | I | Reference | Comment |
---|---|---|---|---|
Capillary | PONA | 595. | Yang, Wang, et al., 2003 | 50. m/0.20 mm/0.50 μm; Program: not specified |
Capillary | Polydimethyl siloxanes | 587. | Zenkevich, 1998 | Program: not specified |
Capillary | Methyl Silicone | 589. | Zenkevich and Kuznetsova, 1990 | Program: not specified |
References
Go To: Top, Gas phase thermochemistry data, Condensed phase thermochemistry data, Phase change data, Reaction thermochemistry data, Gas Chromatography, Notes
Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.
Hubbard, Good, et al., 1958
Hubbard, W.N.; Good, W.D.; Waddington, G.,
The heats of combustion, formation and isomerization of the seven isomeric C4H10S alkane thiols and sulfides,
J. Phys. Chem., 1958, 62, 614-617. [all data]
Hubbard, Katz, et al., 1954
Hubbard, W.N.; Katz, C.; Waddington, G.,
A rotating combustion bomb for precision calorimetry. Heats of combustion of some sulfur-containing compounds,
J. Phys. Chem., 1954, 58, 142. [all data]
McCullough, Scott, et al., 1953
McCullough, J.P.; Scott, D.W.; Finke, H.L.; Hubbard, W.N.; Gross, M.E.; Katz, C.; Pennington, R.E.; Messerly, J.F.; Waddington, G.,
The thermodynamic properties of 2-methyl-2-propanethiol from 0 to 1000°K,
J. Am. Chem. Soc., 1953, 75, 1818-18. [all data]
Cox and Pilcher, 1970
Cox, J.D.; Pilcher, G.,
Thermochemistry of Organic and Organometallic Compounds, Academic Press, New York, 1970, 1-636. [all data]
McCullough, Scott, et al., 1953, 2
McCullough, J.P.; Scott, D.W.; Finke, H.L.; Hubbard, W.N.; Gross, M.E.; Katz, C.; Pennington, R.E.; Messerly, J.F.; Waddington, G.,
The thermodynamic properties of 2-methyl-2-propanethiol from 0 to 1000K,
J. Am. Chem. Soc., 1953, 75, 1818-1824. [all data]
Denyer, Fidler, et al., 1949
Denyer, R.L.; Fidler, F.A.; Lowry, R.A.,
Azeotrope Formation Between Thiols and Hydrocarbons,
Ind. Eng. Chem., 1949, 41, 2727-37. [all data]
McCullough, Scott, et al., 1953, 3
McCullough, J.P.; Scott, D.W.; Finke, H.L.; Hubbard, W.N.; Gross, M.E.; Katz, C.; Pennington, R.E.; Messerly, J.F.; Waddington, G.,
The thermodynamic properties of 2-methyl-2-propanethiol from 0 to 1000 k,
J. Am. Chem. Soc., 1953, 75, 1818-24. [all data]
Majer and Svoboda, 1985
Majer, V.; Svoboda, V.,
Enthalpies of Vaporization of Organic Compounds: A Critical Review and Data Compilation, Blackwell Scientific Publications, Oxford, 1985, 300. [all data]
Reid, 1972
Reid, Robert C.,
Handbook on vapor pressure and heats of vaporization of hydrocarbons and related compounds, R. C. Wilhort and B. J. Zwolinski, Texas A Research Foundation. College Station, Texas(1971). 329 pages.$10.00,
AIChE J., 1972, 18, 6, 1278-1278, https://doi.org/10.1002/aic.690180637
. [all data]
Stockton, Ng, et al., 1998
Stockton, L.D.; Ng, T.L.; Maung, N.; Poole, I.B.; Williams, J.O.; Wright, A.C.; Foster, D.F.; Cole-Hamilton, D.J.,
Dynamic vapour pressure measurements of di-tertiarybutyl sulphide using an ultrasonic monitor,
Journal of Crystal Growth, 1998, 183, 1-2, 95-98, https://doi.org/10.1016/S0022-0248(97)00383-7
. [all data]
Stephenson and Malanowski, 1987
Stephenson, Richard M.; Malanowski, Stanislaw,
Handbook of the Thermodynamics of Organic Compounds, 1987, https://doi.org/10.1007/978-94-009-3173-2
. [all data]
Osborn and Douslin, 1966
Osborn, A.G.; Douslin, D.R.,
Vapor Pressure Relations of 36 Sulfur Compounds Present in Petroleum.,
J. Chem. Eng. Data, 1966, 11, 4, 502-509, https://doi.org/10.1021/je60031a014
. [all data]
Domalski and Hearing, 1996
Domalski, Eugene S.; Hearing, Elizabeth D.,
Heat Capacities and Entropies of Organic Compounds in the Condensed Phase. Volume III,
J. Phys. Chem. Ref. Data, 1996, 25, 1, 1, https://doi.org/10.1063/1.555985
. [all data]
Bartmess, Scott, et al., 1979
Bartmess, J.E.; Scott, J.A.; McIver, R.T., Jr.,
The gas phase acidity scale from methanol to phenol,
J. Am. Chem. Soc., 1979, 101, 6047. [all data]
Wadso, 1957
Wadso, I.,
The heats of hydrolysis of some alkyl thiolesters,
Acta Chem. Scand., 1957, 11, 1745-1751. [all data]
Miller and Bruno, 2003
Miller, K.E.; Bruno, T.J.,
Isothermal Kováts retention indices of sulfur compounds on a poly(5% diphenyl-95% dimethylsiloxane) stationary phase,
J. Chromatogr. A, 2003, 1007, 1-2, 117-125, https://doi.org/10.1016/S0021-9673(03)00958-0
. [all data]
Garbuzov, Misharina, et al., 1985
Garbuzov, V.G.; Misharina, T.A.; Aerov, A.F.; Golovnya, R.V.,
Gas chromatographic retention indices for sulphur(II)-containing organic substances,
J. Anal. Chem. USSR (Engl. Transl.), 1985, 40, 4, 576-586. [all data]
Mikhailova, Gren, et al., 1985
Mikhailova, T.V.; Gren, A.I.; Vysotskaja, L.E.; Misharina, T.A.; Vitt, S.V.; Golovnya, R.V.,
Identification of sulphur-organic compounds obtained by thermal treatment of the meat broths in the presence of alkyl-mercaptopropanol,
Nahrung, 1985, 29, 7, 671-680, https://doi.org/10.1002/food.19850290705
. [all data]
Zygmunt and Staszewski, 1981
Zygmunt, B.; Staszewski, R.,
Retention index and gas chromatographic-mass spectrometric identification of thiols in liquified gas,
Chem. Anal. (Warsaw), 1981, 26, 109-113. [all data]
Golovnya and Garbuzov, 1974
Golovnya, R.V.; Garbuzov, V.G.,
Effect of heteroatom in aliphatic sulfur- and oxygen-containing compounds on the values of the retention indices in gas chromatography,
Izv. Akad. Nauk SSSR Ser. Khim., 1974, 7, 1519-1521. [all data]
Zhu, Wang, et al., 2007
Zhu, X.H.; Wang, W.; Schramm, K.-W.; Niu, W.,
Prediction of the Kova´ ts Retention Indices of Thiols by Use of Quantum Chemical and Physicochemical Descriptors,
Chromatographia, 2007, 65, 11-12, 719-724, https://doi.org/10.1365/s10337-007-0237-3
. [all data]
Safa and Hadjmohannadi, 2005
Safa, F.; Hadjmohannadi, M.R.,
Use of topological indices of organic sulfur compounds in quantitative structure-retention relationship study,
QSAR Comb. Sci., 2005, 24, 9, 1026-1032, https://doi.org/10.1002/qsar.200530008
. [all data]
Yang, Wang, et al., 2004
Yang, Y.; Wang, Z.; Zong, B.; Yang, H.,
Determination of sulfur compounds in fluid catalytic cracking gasoline by gas chromatography with a sulfur chemiluminiscence detector,
Chin. J. Chromatogr., 2004, 22, 3, 216-219. [all data]
Yang, Wang, et al., 2003
Yang, Y.-T.; Wang, Z.; Han. J.-H.; Tian, H.-P.; Yang, H.-Y.,
Determination of sulfur compounds in gasoline fraction of microreactor products by gas chromatography - Atomic emission detector,
Petrochemical Technology (Shiyou Huagong), 2003, 32, 11, 995-998. [all data]
Guevas A.P. and Tellez, 1977
Guevas A.P.; Tellez, J.V.G.,
Determination de mercaptanos de C2 a C4 an muestras gaseosas de hydrocarburos de C4 a C5 por chromatographia en fase vapor,
Revista de Instituto Mexicano di Petroleo, 1977, 9, 1, 85-88. [all data]
Zenkevich, 1998
Zenkevich, I.G.,
The Principle of Structural Analogy in the Calculation of Gas Chromatographic Retention Indices using Physico-Chemical Constants of Organic Compounds,
Zh. Anal. Khim. (Rus.), 1998, 53, 1, 43-49. [all data]
Zenkevich and Kuznetsova, 1990
Zenkevich, I.G.; Kuznetsova, L.M.,
Logic Criteria on Prediction of Gas Chromatographic Retention Indices from Physico-Chemical Properties of Organic Compounds,
Dokl. Akad. Nauk SSSR, 1990, 315, 4, 881-885. [all data]
Notes
Go To: Top, Gas phase thermochemistry data, Condensed phase thermochemistry data, Phase change data, Reaction thermochemistry data, Gas Chromatography, References
- Symbols used in this document:
Cp,liquid Constant pressure heat capacity of liquid S°liquid Entropy of liquid at standard conditions Tboil Boiling point Tc Critical temperature Tfus Fusion (melting) point Ttriple Triple point temperature ΔHtrs Enthalpy of phase transition ΔStrs Entropy of phase transition ΔcH°liquid Enthalpy of combustion of liquid at standard conditions ΔfH°gas Enthalpy of formation of gas at standard conditions ΔfH°liquid Enthalpy of formation of liquid at standard conditions ΔfusH Enthalpy of fusion ΔfusS Entropy of fusion ΔrG° Free energy of reaction at standard conditions ΔrH° Enthalpy of reaction at standard conditions ΔvapH Enthalpy of vaporization ΔvapH° Enthalpy of vaporization at standard conditions - Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
- The National Institute of Standards and Technology (NIST) uses its best efforts to deliver a high quality copy of the Database and to verify that the data contained therein have been selected on the basis of sound scientific judgment. However, NIST makes no warranties to that effect, and NIST shall not be liable for any damage that may result from errors or omissions in the Database.
- Customer support for NIST Standard Reference Data products.