Electrografting refers to the electrochemical reaction that permits organic layers to be attached to solid conducting substrates. This definition can be extended to reactions involving an electron transfer between the substrate to be modified and the reagent, but also to examples where a reducing or oxidizing reagent is added to produce the reactive species. These methods are interesting as they provide a real bond between the surface and the organic layer. Electrografting applies to a variety of substrates including carbon, metals and their oxides, but also dielectrics such as polymers. Since the 1980s several methods have been developed, either by reduction or oxidation, and some of them have reached an industrial stage. This critical review describes the methods that are used for electrografting, their mechanism, the formation and growth of the layers as well as their applications (742 references).

Electrografting: a powerful method for surface modification

A novel energetic cocrystal predicted to exhibit greater power and similar sensitivity to that of the current military standard explosive 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) is presented. The cocrystal consists of a 2:1 molar ratio of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), a powerful explosive too sensitive for military use, and HMX. A predicted detonation velocity 100 m/s higher than that of β-HMX, the most powerful pure form of HMX, was calculated for the cocrystal using Cheetah 6.0. In small-scale impact drop tests the cocrystal exhibits sensitivity indistinguishable from that of β-HMX. This surprisingly low sensitivity is hypothesized to be due to an increased degree of hydrogen bonding observed in the cocrystal structure relative to the crystals of pure HMX and CL-20. Such bonding is prevalent in this and other energetic cocrystals and may be an important consideration in the design of future materials. By being more powerful and safe to handle, the cocrys...

High Power Explosive with Good Sensitivity: A 2:1 Cocrystal of CL-20:HMX

Potassium t-butoxide alone can promote the biaryl coupling of electron-deficient nitrogen heterocycles and haloarenes.

Synthesis of polyazapolycyclic caged polynitramines

Arene diazonium salts are common, easily prepared and highly useful intermediates in organic synthesis due to their rich reactivity and diverse transformations. In this review, recent advances involving arene diazonium salts as starting materials or active intermediates for various synthetically useful applications are summarized.

Recent applications of arene diazonium salts in organic synthesis.

The synthesis of biaryl compounds by means of the diazo reaction

cisand tr~lzs-A~*~7-Pregnadiene-3 @,20-diol Diacetates (VII, VIII) .-A solution of 4.4 g. of A6-pregnene-3@-ol-20one and 2.45 g. of p-toluenesulfonic acid in 500 cc. of acetic anhydride was boiled gently and the solvent allowed to distil. After about seven hours the residual dark solution (100-150 cc.) was poured into ice-water, and after a short interval the product was extracted with ether and the solution was washed with water, sodium carbonate solution, and again with water, dried and evaporated. The residue (5.06 g.) was dissolved in a small amount of benzene and the solution diluted with 150 cc. of petroleum ether (30-60\"), chromatographed on alumina, and eluted with petroleum ether, benzene-petroleum ether (1 : 2 and 1 : 1) and with benzene. The initial crystalline fractions melting over the range 120-133\" were combined and on repeated crystallization from methanol gave enol acetate-A as long prisms, m. p. 144-146\" (1.84 g., 33%). 6 sample recrystallized again for analysis melted a t 147 , [ c Y ] ~ ~ D -50.0' ( C = 2% in chloroform). Anal. Calcd. for C2&804: C, 74.95; H, 9.06. Found: C, 74.82; H, 9.01. Processing of later chromatographic fractions and of mother liquor material by further chromatography and recrystallization from methanol eventually afforded 0.22 g. of pure enol acetate-B, as plates, m. p. 171-172\", [ C Y ] ~ ~ D 52' ( C = 2% in chloroform). Anal. Calcd. for C2jH3804: C, 74.95; H, 9.06. Found: C, 74.58; H, 8.94. The methanol mother liquors afforded 1.2 g. of a mixture of A and B, m. p. 115-117\", that showed no depression when mixed with either isomer. Bromination of Enol Acetate-A (m. p. 147 \").-A solution of 0.08 g. of bromine in chloroform was added dropwise a t room temperature to a solution of 0.1 g. of A in 5 cc. of chloroform. Removal of the solvent in vacuum and crystallization from acetone-ligroin (70-9; \") gave 90 mg. (SOPl,) of bromo product melting at 162 , dec. Recrystallization from the same solvent gave pure material in the form of plates, m. p . 166-168\", dec. Plattner and coworkers7 have reported the preparation of 3 P-acetoxy-20keto-5,6,17-tribromopregnae (IX) by bromination of pregnenolone acetate, but they report merely the melting point 149-151' and give no analysis. We prepared the tribromo compound according to their procedure and on repeated recrystallization from acetone-ligroin formed plates, m. p. 167-168\", dec., that gave no depression when mixed with the substance from enol acetate-A. Anal. Calcd. for C23H3303Rr3: C, 46.25; H, 5..56. Found: C, 46.26; H , 5.38. The bromination of isomer-A was conducted more conveniently in acetic acid; dilution with water precipitated the product and one crystallization from acetone-ligroin gave plates, m. p. 161-162\" in 7170 yield. The fully purified sample melted a t 166-167' dec., and gave no depression with either of the above samples. Bromination of Enol Acetate-B (M. p. 171 \") .-Bromination in acetic acid as above gave plates, m. p., arid mixed m. p. with the product from A , 167-168\", dec. Anal. Calcd. for C23H3303Br~: C, 46.26; H, 6.56. Found: C, 46.19; H, 5.31. Saponification of the Enol Acetates.-A solution of 0.1 g . of isomer A or B in 10 cc. of methanol was treated with a solution of 0.1 g. of potassium carbonate in 1 cc. each of water and methanol and let stand a t room temperature for five hours. The product, precipitated by water, on crystallization from dilute alcohol gave plates identified bv crvstal form. m. D. and mixed m. D . 1189-190\") as Ai-pregnene-3P-ol-20-bne; yield, 60 mg. (76%) from A, 58 mg. (73%) from B. Saponification of 30 mg. of A or B in 4 cc. of methanol was also conducted by adding a solution of 30 mg. of potassium bicarbonate in a few drops of water and 2 cc. of methanol. After forty-eight hours a t room temperature, processing as above gave crude pregnenolone, m. p. 184188': 19.5 mg. (82Oj,) from A, and 19.0 mg. (80%) from B. The recrystallized samples had the m. p. and mixed m. p. 189-190\".

W. E. Bachmann

Papers

The synthesis of biaryl compounds by means of the diazo reaction

A New Method of Preparing the High Explosive RDX

The Total Synthesis of the Sex Hormone Equilenin and Its Stereoisomers

The total synthesis of the sex hormone equilenin

The coupling of derivatives of polycyclic hydrocarbons with glycine