In organic chemistry, a thial or thioaldehyde is a functional group which is similar to an aldehyde, RC(O)H, in which a sulfur (S) atom replaces the oxygen (O) atom of the aldehyde (R represents an alkyl or aryl group).[1] Thioaldehydes are even more reactive than thioketones. Unhindered thioaldehydes are generally too reactive to be isolated — for example, thioformaldehyde, H2C=S, condenses to the cyclic trimer 1,3,5-trithiane. Thioacrolein, H2C=CHCH=S, formed by decomposition of allicin from garlic, undergoes a self Diels-Alder reaction giving isomeric vinyldithiins.[2][3] While thioformaldehyde is highly reactive, it is found in interstellar space along with its mono- and di-deuterated isotopologues.[4] With sufficient steric bulk, however, stable thioaldehydes can be isolated.[5]
In early work, the existence of thioaldehydes was inferred by trapping processes. For instance the reaction of Fc2P2S4 with benzaldehyde was proposed to form thiobenzaldehyde, which forms a cycloadduct with the dithiophosphine ylides to form a C2PS3 ring.[7]
↑N. Takeda; N. Tokitoh; R. Okazaki (1997). "Synthesis, Structure, and Reactions of the First Rotational Isomers of Stable Thiobenzaldehydes, 2,4,6-Tris[bis(trimethylsilyl)methyl]thiobenzaldehydes". Chemistry: A European Journal. 3: 62–69. doi:10.1002/chem.19970030111.
↑A. Capperucci; A. Degl’Innocenti; P. Scafato; P. Spagnolo (1995). "Synthetic Applications of Bis(trimethylsilyl)sulfide: Part II. Synthesis of Aromatic and Heteroaromatic o-Azido-Thioaldehydes". Chemistry Letters. 24 (2): 147. doi:10.1246/cl.1995.147.
