4-Acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium Tetrafluoroborate

[219543-09-6] C11H21N2O2F4B (MW 300.09) InChI = 1S/C11H20N2O2.BF4/c1-8(14)12-9-6-10(2,3)13(15)11(4,5)7-9;2-1(3,4)5/h9H,6-7H2,1-5H3;/q;-1/p+1 InChIKey = HTMHEICBCHCWAU-UHFFFAOYSA-O [219543-09-6] C11H21N2O2F4B (MW 300.09) InChI = 1S/C11H20N2O2.BF4/c1-8(14)12-9-6-10(2,3)13(15)11(4,5)7-9;2-1(3,4)5/h9H,6-7H2,1-5H3;/q;-1/p+1 InChIKey = HTMHEICBCHCWAU-UHFFFAOYSA-O 4-Acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborat 1, a, X = BF4− [219543-09-6] C11H21N2O2F4B (MW 300.10)3 InChI = 1S/C11H20N2O2.BF4/c1-8(14)12-9-6-10(2,3)13(15)11(4,5)7-9;2-1(3,4)5/h9H,6-7H2,1-5H3;/q;-1/p+1 InChIKey = HTMHEICBCHCWAU-UHFFFAOYSA-O 4-Acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium perchlorate 1, b, X = ClO4− [219543-08-5] C11H21N2O6Cl (MW 312.72)3, 13 InChI = 1S/C11H20N2O2.ClHO4/c1-8(14)12-9-6-10(2,3)13(15)11(4,5)7-9;2-1(3,4)5/h9H,6-7H2,1-5H3;(H,2,3,4,5) InChIKey = QPNXYTPYENYALX-UHFFFAOYSA-N 2,2,6,6-Tetramethylpiperidine-1-oxoammonium tetrafluoroborate 10a, X = BF4− [33247-78-8] C9H18NOF4B (MW 243.05)14 InChI = 1S/C9H18NO.BF4/c1-8(2)6-5-7-9(3,4)10(8)11;2-1(3,4)5/h5-7H2,1-4H3;/q+1;-1 InChIKey = GAJDGWHXJQBONI-UHFFFAOYSA-N 2,2,6,6-Tetramethylpiperidine-1-oxoammonium perchlorate 10b, X = ClO4− [31198-93-3] C9H18NO5Cl (MW 255.09)14, 15 InChI = 1S/C9H18NO.ClHO4/c1-8(2)6-5-7-9(3,4)10(8)11;2-1(3,4)5/h5-7H2,1-4H3;(H,2,3,4,5)/q+1;/p-1 InChIKey = CPLCZRHFOLVQQN-UHFFFAOYSA-M 2,2,6,6-Tetramethylpiperidine-1-oxoammonium chloride 10c, X = Cl− [26864-01-7] C9H18NOCl (MW 191.70)16 InChI = 1S/C9H18NO.ClH/c1-8(2)6-5-7-9(3,4)10(8)11;/h5-7H2,1-4H3;1H/q+1;/p-1 InChIKey = UXJJNTSDDNCDLD-UHFFFAOYSA-M 2,2,6,6-Tetramethylpiperidine-1-oxoammonium bromide 10d, X = Br− [85917-27-7] C9H18NOBr (MW 236.15)17 InChI = 1S/C9H18NO.BrH/c1-8(2)6-5-7-9(3,4)10(8)11;/h5-7H2,1-4H3;1H/q+1;/p-1 InChIKey = PJAVCFQMWXUNQV-UHFFFAOYSA-M 4-Methoxy-2,2,6,6-tetramethylpiperidine-1-oxoammonium-tetrafluoroborate 11a, X = BF4− [135023-09-5] C10H20NO2F4B (MW 273.07)18 InChI = 1S/C10H20NO2.BF4/c1-9(2)6-8(13-5)7-10(3,4)11(9)12;2-1(3,4)5/h8H,6-7H2,1-5H3;/q+1;-1 InChIKey = YIZRNAPYVZDWEL-UHFFFAOYSA-N 4-Methoxy-2,2,6,6-tetrame-thylpiperidine-1-oxoammonium chloride 11b, X = Cl− [95407-70-8] C10H20NO2Cl (MW 221.72)19 InChI = 1S/C10H20NO2.ClH/c1-9(2)6-8(13-5)7-10(3,4)11(9)12;/h8H,6-7H2,1-5H3;1H/q+1;/p-1 InChIKey = XTQPMZGDXUYFLV-UHFFFAOYSA-M 4-Methoxy-2,2,6,6-tetram-ethylpiperidine-1-oxoammonium bromide 11c, X = Br− [90246-27-8] C10H20NO2Br (MW 266.17)19 InChI = 1S/C10H20NO2.BrH/c1-9(2)6-8(13-5)7-10(3,4)11(9)12;/h8H,6-7H2,1-5H3;1H/q+1;/p-1 InChIKey = IMQPWXWUDKGRRG-UHFFFAOYSA-M (reagent used to oxidize alcohols to aldehydes or ketones. Of special interest, allyl alcohols can be oxidized without isomerization and phenolic benzyl alcohols can be oxidized without blocking the phenol group; all of these reagents have been used for the oxidation of primary and secondary alcohols to aldehydes or ketones, respectively. They also have a certain number of additional minor oxidation reactions. Many other salts are known1) Physical Data: mp 195–196 °C dec (Kofler). 1, a, mp 193–194 °C (dec.); 1b, mp 177–178 °C (dec.); 10a, mp 162–163 °C; 10b, mp 157–158 °C; 10c, mp 118–119 °C; 10d, mp 76–78 °C; 11a, mp 162–162.5 °C; 11b, mp 121–123 °C; 11c, mp 206–207 °C. Solubility: partially soluble in water (6 g/100 mL at 0 °C, 8 g/100 mL at 20 °C, and about 100 g/100 mL at 100 °C; reacts very slowly with hot water), slightly soluble in methylene chloride (0.04 g/100 mL at 20 °C). 1a and 1b are slightly soluble in water and methylene chloride, while insoluble in ether; 10a–10d are insoluble in ether; 11a–11c are insoluble in carbon tetrachloride. Otherwise, solubilities are variable. Most reactions are carried out in methylene chloride, less often in acetonitrile. Form Supplied in: all of these salts are prepared from the corresponding parent nitroxides, 5, 12, and 13, which are commercially available. None of the salts are commercially available currently. Preparative Methods: in a slightly modified procedure,3 100 g of 4-acetylamino-2,2,6,6-tetramethyl-1-piperidineoxyl (0.469 mol) is stirred with 50 mL of H2O, and 90 g of 48% aqueous HBF4 (0.492 mol) is added over about 1 h. The mixture is placed in an ice bath, and 332.2 g of commercial bleach (5.25% NaOCl, 0.235 mol) is added over about 2 h. The mixture is allowed to stir in ice for about 3 h and then filtered. The solid bright yellow salt is pressed as dry as possible and washed with two 50-mL portions of ice water and two 100-mL portions of CH2Cl2. The salt is dried at room temperature and in air to constant weight to give 90–95 g (about 65%) of the reagent, mp 195–196 °C. Further drying in a vacuum desiccator reduced the weight only slightly. For recovery of the remainder of the salt, the combined filtrates (water and CH2Cl2) are treated with 20 g of NaHCO3 and 20 mL of 95% ethanol to reduce the oxoammonium salt to the starting nitroxide. The layers are separated and the aqueous phase is extracted with three 50-mL portions of CH2Cl2. The extracts are combined, dried over MgSO4, and evaporated to give 25–30 g of nitroxide, mp 145–147 °C, suitably pure for the preparation of more oxoammonium salt. Oxoammonium salts are prepared from commercially available, nitroxide free radicals, 5, 12, and 13. There are essentially two methods for the preparation of the oxoammonium salts from nitroxides. The first is based on the acid-catalyzed disproportionation of nitroxide in strong acid as shown for 1a in eq 1.14, 20 The method has been used both in water and dry ether for the preparation of many oxoammonium salts. The second is based on the halogens as shown for 11b in eq 2.16, 19 In the halide reactions, the elemental halogens act both as oxidizing agents and the source of the anions. 4-acetylamino-2,2,6,6-tetramethyl-1-piperidineoxyl(4-acetylamino-TEMPO)[14691-89-5] InChI = 1S/C11H21N2O2/c1-8(14)12-9-6-10(2,3)13(15)11(4,5)7-9/h9H,6-7H2,1-5H3,(H,12,14) InChIKey = UXBLSWOMIHTQPH-UHFFFAOYSA-N 2,2,6,6-tetramethyl-1-piperidineoxyl(TEMPO)[2564-83-2] InChI = 1S/C9H18NO/c1-8(2)6-5-7-9(3,4)10(8)11/h5-7H2,1-4H3 InChIKey = QYTDEUPAUMOIOP-UHFFFAOYSA-N 4-methoxy-2,2,6,6-tetramethyl-1-piperidineoxyl(4-methoxy-TEMPO)[95407-69-5] InChI = 1S/C10H20NO2/c1-9(2)6-8(13-5)7-10(3,4)11(9)12/h8H,6-7H2,1-5H3 InChIKey = SFXHWRCRQNGVLJ-UHFFFAOYSA-N (1) (2) The preparation of 1a and its applications are described in a tested procedure in Organic Syntheses.20 The procedure involves the use of a second oxidant, bleach, to increase the yield of salt. Purity: recrystallized, if necessary, from an equal weight of water. Solution heated and cooled as rapidly as possible. The purity of the salt can be assayed using 1-decanol as substrate. It is normally close to 100%. Handling, Storage, and Precautions: the salt (tetrafluoroborate) is non-hygroscopic and indefinitely stable. No hazards are known. For anhydrous reactions, the previously dried salt can be dried in a vacuum over P2O5 at 35 °C, although the reduc- tion in weight is slight. The perchlorate salts 1b and 10b have been used extensively,3 but since 1b detonated on drying under vacuum,13 they should both be avoided. Compound 1a appears to be nonhygroscopic, stable indefinitely, and to have ideal solubility properties in methylene chloride. For these reasons, it will be the main theme of this article. The other salts have various degrees of instabilities and some are quite hygroscopic. It should be understood that the other oxoammonium salts have similar properties. Nothing is known about their toxicity.