Yes, you are correct: “lit.” refers to the literature value.
Usually one would also expect the corresponding reference, but it looks like Merck doesn't attach any to the provided data directly in place.
From The ACS Style Guide, section Reporting Analytical Data [1, p. 274] (emphasis mine):
Melting and Boiling Points
mp 175.5 °C (lit.25 mp 175–176 °C)
mp 225 °C dec
bp 127 °C
Abbreviations: mp, melting point; bp, boiling point; lit., literature value; and dec, decomposition.
A full space is used between the number and the unit °C; the degree symbol is closed up to the C.
A superscript number after “lit.” denotes the number of the reference.
The CSE Style Guide also recognizes “lit.” as abbreviation for literature in Appendix 29.2 Common English words used in bibliographic description and their abbreviations [2, p. 645], further referring to ISO 832:1994.
- The ACS Style Guide: Effective Communication of Scientific Information, 3rd ed.; Coghill, A. M., Garson, L. R., Eds.; American Chemical Society; Oxford University Press: Washington, DC; Oxford; New York, 2006. ISBN 978-0-8412-3999-9.
- Scientific Style and Format: The CSE Manual for Authors, Editors, and Publishers, 8th ed.; Council of Science Editors, Ed.; Council of Science Editors; London: in cooperation with The University of Chicago Press: Chicago, 2014. ISBN 978-0-226-11649-5.