Reductive electrochemical formation of 6H-dibenzo[b,d]pyran-6-one and 2-benzopyran-1(1H)-one

In the present Letter several carbolactones (oxidative products) are obtained under aprotic cathodic conditions in the preparative scaled electrolysis of 1,2-quinones in a divided electrochemical cell and in the presence of oxygen. When 9,10-phenanthrenequinone is reduced 6H-dibenzo[b,d]pyran-6-one and [1,1′-biphenyl]-2,2′-dicarboxylic acid are obtained as major products. In the reduction of 1,2-naphthoquinone, 2-benzopyran-1(1H)-one, and 2-(2-carboxyethenyl)-benzoic acid were formed as main products. The proposed mechanism to explain the formation of these and other products, that involves an electron-transfer reaction to the oxygen in air, is now discussed.

Aviation unit and intermediate maintenance repair parts and special tools list (including depot maintenance repair parts and special tools) for helicopter, utility - tactical transport, UH-1B, UH-1C, UH-1H, UH-1M, EH-1H (Bell), UH-1V, NSN 1520-00-713-9912 (UH-1B), 1520-00-997-8862 (UH-1C), 1520-00-087-7637 (UH-1H), 1520-00-809-2631 (UH-1M), 1520-00-368-8442 (EH-1H), 1520-01-043-4949 (UH-1V).

"27 February 1981"--[Vol. 1].

Aviation unit and intermediate maintenance instructions : Army model UH-1H/V/EH-1H/X helicopters.

"30 September 1987."

Operator's manual : boring machine, engine cylinder (Rottler Boring Bar Company, model no. DA-1H) (4910-473-6361).

"November 1964."

Direct support and general support maintenance repair parts and special tools list for electronics equipment configuration, Army models UH-1H and UH-1V with SLAE.

Includes index.

Organizational maintenance manual : electronic equipment configurations, Army model UH-1H helicopter (with standard lightweight avionics equipment) (NSN 1520-00-057-7637).

Includes index.

Direct support and general support maintenance repair parts and special tools list ... for electronic equipment configuration, Army models UH-1D (NSN 1520-00-859-2670), UH-1H (NSN 1520-00-087-7637), UH-1V (NSN 1520-01-043-4949), and EH-1X (aircraft) (NSN 1520-01-042-9396) helicopters.

"17 May 1985."

UH-1H/V helicopter : operator's manual /

Includes index.

Aviation unit and intermediate maintenance instructions : Army model UH-1H/V/EH-1H/X helicopters.

"20 September, 1987."

Aviation unit and intermediate maintenance repair parts and special tools list (including depot maintenance repair parts and special tools) for helicopter, utility - tactical transport, UH-1B, UH-1C, UH-1H, UH-1M, EH-1H (Bell), UH-1V, NSN 1520-00-713-9912 (UH-1B), 1520-00-997-8862 (UH-1C), 1520-00-087-7637 (UH-1H), 1520-00-809-2631 (UH-1M), 1520-00-368-8442 (EH-1H), 1520-01-043-4949 (UH-1V).

"27 February 1981"--[Vols. 1-2].

UH-1H/V and EH-1H/X aircraft, phased maintenance checklist.

"4 January 1983."

Aviation unit and intermediate maintenance instructions : Army model UH-1H/V/EH-1H/X helicopters.

"30 September 1987"--[Vol. 1].