HO OH ______OH
HO{_____}--------CO--------{______}OH
COOH OH
[Diagonal bond between HO and COOH on left.]

The ketone formula was corroborated by Nierenstein, [Footnote: _Ber._
1905, 38, 3641.] who distilled tannin with zinc dust and obtained
diphenylmethane (smell of benzene) and a crystalline product,
M.P. 7O -71 C. (M.P. of diphenyl = 71 C.). Konig and Kostanecki
[Footnote: _Ibid._, 1906, 39, 4027.] sought to find the constitution of
the tannins in the leuco-compounds of the oxyketones, to which catechin
belongs. Nierenstein (see above), however, emphasises that the high
molecular weight and the optical activity speak against the digallic
acid formula, but in favour of this are the following points: (1) the
decomposition of tannin with the formation of gallic acid; (2) the
decomposition of methylotannin with the formation of di- and trimethyl
esters of gallic acid; and (3) the production of diphenylmethane on
distillation with zinc dust. The latter reaction especially illustrates
the analogous formation of fluorene from compounds of the type--

--CO.O
^ ______ ^
| | | |
| | | |
V V

Nierenstein gave the name "Tannophor" to the mother-substance of tannin,
phenylbenzoate, C_6H_5-COO-C_6H_5.