thial

{{Short description|1=Chemical group (–CH=S)}}

File:Thial-2D-general-structural-formula.png

In organic chemistry, a thial or thioaldehyde is a functional group which is similar to an aldehyde, {{chem2|RC(O)H}}, in which a sulfur (S) atom replaces the oxygen (O) atom of the aldehyde (R represents an alkyl or aryl group). Thioaldehydes are even more reactive than thioketones. Unhindered thioaldehydes are generally too reactive to be isolated — for example, thioformaldehyde, {{chem2|H2C\dS}}, condenses to the cyclic trimer 1,3,5-trithiane. Thioacrolein, {{chem2|H2C\dCHCH\dS}}, formed by decomposition of allicin from garlic, undergoes a self Diels-Alder reaction giving isomeric vinyldithiins.{{cite journal | journal = Chemical Physics Letters | volume = 29 | issue = 2 | year = 1974 | pages = 265–269 | title = The photoelectron and microwave spectra of the unstable species thioacetaldehyde, CH 3CHS, and thioacetone, (CH 3) 2CS |author1=H. W. Kroto |author2=B. M. Landsberg |author3=R. J. Suffolk |author4=A. Vodden | doi = 10.1016/0009-2614(74)85029-3 | bibcode=1974CPL....29..265K}}{{cite book|author=E. Block|title=Garlic and Other Alliums: The Lore and the Science|url=https://books.google.com/books?id=6AB89RHV9ucC|publisher=Royal Society of Chemistry|year=2010|isbn=978-0-85404-190-9}} While thioformaldehyde is highly reactive, it is found in interstellar space along with its mono- and di-deuterated isotopologues.{{Cite web|url=http://www.astro.uni-koeln.de/site/vorhersagen/molecules/ism/H2CS.html|title = CDMS}} With sufficient steric bulk, however, stable thioaldehydes can be isolated.{{cite journal |author1=N. Takeda |author2=N. Tokitoh |author3=R. Okazaki | title = Synthesis, Structure, and Reactions of the First Rotational Isomers of Stable Thiobenzaldehydes, 2,4,6-Tris[bis(trimethylsilyl)methyl]thiobenzaldehydes | journal = Chemistry: A European Journal | year = 1997 | volume = 3 | pages = 62–69 | doi = 10.1002/chem.19970030111}}

In early work, the existence of thioaldehydes was inferred by trapping processes. For instance the reaction of {{chem2|Fc2P2S4}} with benzaldehyde was proposed to form thiobenzaldehyde, which forms a cycloadduct with the dithiophosphine ylides to form a {{chem2|C2PS3}} ring.{{cite journal| title = Synthetic Applications of Bis(trimethylsilyl)sulfide: Part II. Synthesis of Aromatic and Heteroaromatic o-Azido-Thioaldehydes|author1=A. Capperucci |author2=A. Degl’Innocenti |author3=P. Scafato |author4=P. Spagnolo | journal = Chemistry Letters| volume = 24| pages = 147| year = 1995| doi = 10.1246/cl.1995.147| issue = 2}}