Ep 1 854 797 A1

(19) &

(11) EP 1 854 797 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: (51) Int Cl.: 14.11.2007 Bulletin 2007/46 C07D 487/16 (2006.01)

(21) Application number: 06384011.0

(22) Date of filing: 02.05.2006

(84) Designated Contracting States: • Jiménez Alonso, Oscar AT BE BG CH CY CZ DE DK EE ES FI FR GB GR 08006 Barcelona (ES) HU IE IS IT LI LT LU LV MC NL PL PT RO SE SI •Holenz, Jörg SK TR Lab. del Dr. Esteve, S.A. Designated Extension States: 08041 Barcelona (ES) AL BA HR MK YU • Corbera Arjona, Jordi Lab. del Dr. Esteve, S.A. (71) Applicant: ISDIN, S.A. 08041 Barcelona (ES) 08006 Barcelona (ES) • Payella, David 08030 Barcelona (ES) (72) Inventors: • Pelejero, Carles • Schwarz, Marcus 08030 Barcelona (ES) Leipzigerstr. 29 • Trullas, Carles Ramón 09596 Freiberg (ES) 08030 Barcelona (ES) • Buschmann, Helmut H. Lab. del Dr. Esteve, S.A. (74) Representative: Barlocci, Anna et al 08041 Barcelona (ES) ZBM Patents • Kroke, Edwin Zea, Barlocci & Markvardsen Leipziger Str. 29, 09596 Freiberg (DE) C/ Balmes, 114 - 4T 08008 Barcelona (ES)

(54) Process for preparing cyameluric chloride

(57) The present invention concerns an improved process for obtaining larger quantities (several 10 grams up to kilograms) of pure cyameluric chloride (I) by chlo-

rination of cyameluric acid (C6N7(OH)3) or its alkaline salts followed by fractioned vacuum sublimation. EP 1 854 797 A1

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Description tives for rocket propellants (see US 3,202,659), stabiliz- ers for photographic emulsions (see US 2,704,716 and FIELD OF THE INVENTION US 2,801,172), dyes (see DE 1,102,321), graphitic C3N4 structures as a suitable precursors of superhard C3N4 [0001] The present invention concerns an improved 5 phases (see Kroke,E.; New J. Chem.; (2002); 26; process for obtaining larger quantities (several 10 grams 508-512). It also is an intermediate for the preparation of up to kilograms) of pure cyameluric chloride (I) by chlo- several variously usable heptazine derivatives that has rination of cyameluric acid (C6N7(OH)3) or its alkaline been pointed out elsewhere (see Pauling,L.; Proc. Nat. salts followed by fractioned vacuum sublimation. 2,5,8- Acad. Sci. US; (1937); 23; 615-620; DE 2,106,675; US trichloro-1,3,4,6,7,9,9b-heptaazaphenalene of the for- 10 4,205,167; furthermore Finkel’shtein,A.L.; Russ. Chem. mula (I) Rev.; (1964); 33(7); 400-405). [0005] At present two fundamentally different procedures are known for obtaining the cyameluric chloride of formula (I). On one hand compound (I) is obtained by 15 reaction of C6N7O3(R)3, cyameluric acid (when R=H) or an alkaline cyamelurate (when R=Na, K, etc) with phosphorous pentachloride in a closed system (see Rede- mann,C.E.; J. Am. Chem. Soc.; (1940); 62; 842-846). In this original procedure, done in solid state without any 20 solvent or liquid phase in a sealed tube at 230 °C, a pressure develops due to formation of volatile POCl3 and, in order to avoid bursting of the ampoule, the reaction had therefore occasionally to be interrupted and the positive pressure to be discharged. 25 [0006] In a later work of Schroeder and Kober (see Schroeder,H.; J. Org. Chem.; (1962); 27; 4264) it is reported that the reaction using a sealed bomb tube did not have to be interrupted and that after finishing and upon opening of the tube no positive pressure was de- 30 tectable. Attempts to avoid the use of a sealed system is also known as 2,5,8-trichlorotri-s-triazine and desig- by replacing the PCl5 with phenylphosphorous tetrachlo- nated as cyameluric chloride in this invention. ride (C6H4PCl4) were not successful. [0007] According to Neeff (see DE 1,102,321) it is pos- BACKGROUND OF THE INVENTION sible to perform the chlorination in an open system using 35 boiling o-dichlorobenzene as a reaction medium or sol- [0002] Aromatic nitrogen heterocycles have a wide va- vent. However, aromatic chlorinating solvents are fre- riety of uses in coordination chemistry and optical sci- quently carcinogens. They are difficult to be completely ence. In this sense, s-triazine is widely used in synthetic removed from the product due to their relatively low vol- chemistry, coordination chemistry and optical and mag- atility and high affinity to the aromatic π-system of the netic studies, also is playing a key role in molecular routes 40 heptazine. Such contamination is particularly problemat- to carbon nitride (CNx) materials. On the other hand hav- ic, if the final product synthetized from the cyameluric ing as final objective to incorporate larger C-N fragments chloride is to be used in a human environment. in precursors of this aromatic nitrogen heterocycles, one [0008] The separation of side products of the chlorin- of the most studied ones has been the 1,3,4,6,7,9,9b- ation (phosphoryl chloride POCl3, alkali chloride and pos- heptaazaphenalene ring system (also known as tri-s-tri- 45 sibly phosphates) was accomplished by both proce- azine or s-heptazine) (see Miller,D.R.; J. Am. Chem. dures, Redemanns and Schroeder, via washing with wa- Soc.; (2004); 126; 5372-5373). ter followed by vacuum filtration. This is disadvanta- [0003] In this way, the "azaaromatic chlorides" which geous, since cyameluric chloride is very sensitive to hy- are defined as aromatic compounds containing many drolysis. Even when ice water at 0°C is used (see C=N-Cl subunits, represents a remarkable class of inter- 50 Schroeder procedure) a large part of the product is de- mediates which display extensive networks of intermo- composed to form cyameluric acid. lecular nitrogen-chloride donor-acceptor interactions in [0009] Own attempts of the inventors indicated that the the solid state as has been described in the literature fine particle size of the cyameluric chloride caused long (see Xu, K.; J. Am. Chem. Soc.; (1994); 116; 105). filtration times. This implies - in combination with the re- [0004] Cyameluric chloride is a valuable intermediate 55 sidual moisture of the filter cake - a problem, to which for the synthesis of different derivatives, such as gelling also by use of a filter press as well as immediate evac- agents for aliphatic hydrocarbons (see US 3,089,875), uation of the filter cake in a desiccator over phosphorous fluorine-containing oxidants which can be used as addi- pentoxide could not be solved satisfactorily.

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[0010] Further attempts to purify the product by subli- [0017] In one preferred embodiment the method ap- mation under atmospheric pressure and with high vacu- plied for removing melamine as well as other molecular um were not successful according to Redemann refer- cyanamide derivatives from the starting material is by ence. pyrolysis that is carried out applying the following tem- [0011] Experiments of the inventors with a commercial 5 perature scheme: sublimation set-up consisting of a vacuum recipient and a water-cooled separating surface, confirmed these find- a. heating from room temperature to between 100 ings. °C and 200°C, preferably from room temperature to [0012] Pure cyameluric chloride can be obtained by a 120 °C in 60 minuts, preferably in 30 minutes procedure described by Gremmelmaier (see US 10 b. maintain between 100 °C and 200°C, preferably 4,205,167). In this patent, chlorine cyanide CI-CN or maintain 120 °C during at least 2 hours, preferably evaporated cyanuric chloride is transferred to a cyame- during 4 hours luric chloride under addition of atmospheric oxygen at an c. heating from between 100 °C and 200°C to be- activated charcoal catalyst at 400 °C. The cyameluric tween 400 °C and 800°C, preferable from 120 °C to chloride which is formed is obtained as a mixture with 15 560 °C in between 1 and 3 hours, preferably in 2 remaining starting material cyanuric chloride. The prod- hours uct is collected in a flask which is heated to 200 °C, while d. maintain between 400 °C and 800°C, preferably the cyanuric chloride condenses in another flask at 20 maintain 560 °C during at least 1 hour, preferably °C. This procedure is characterized by the following dis- during 2 hours followed by cooling down. advantages: relative low yield (31.7 mass percentatge of 20 the cyanuric chloride used as starting material), relatively [0018] In another embodiment the method applied for complicated set-up because mass flow controllers are removing melamine as well as other molecular cyana- required for controlling the amount of starting material mide derivatives from the starting material is via Soxhlet- and air, difficult adjustment of the evaporation rate of solid extraction with water during at least 24 hours, preferably cyanuric chloride and a multiple zone furnace and/or sev- 25 during 48 hours and posterior evaporation of the resulting eral furnaces with separate regulation, arranged into a aqueous solution by known means as rotation evapora- row and connected with joints which have to be heated tor. to >200 °C are necessary in order to prevent condensa- [0019] Finally in another embodiment the method ap- tion of the product which might cause problems with the plied for removing melamine as well as other molecular tightness of the glass joint between the reactor and the 30 cyanamide derivatives from the starting material is via receptacles, specially the temperature stability of the extraction with water, preferably at temperatures up to used sealing material. 85 °C. [0020] In particular melamine otherwise causes prob- DISCLOSURE OF THE INVENTION lems during the following process steps as impurities in 35 x the form of cyanurates such as (H3-xC3N3O3) or cyanuric [0013] The present invention includes several im- chloride. The latter leads, due to its higher vapour pres- provements on conditioning of the raw material, the chlo- sure to a poorer vacuum during the double sublimation rination and the purification of the final product. It was used to obtain the final product, and thereby to signifi- found that a commercially available technical product, cantly decreased yields per time unit. 40 the polymer melon (designated as melon powder in this [0021] The chlorination of C6N7O3(R)3 (with R as de- invention and identified with CAS RN: 32518-77-7), can fined above) is preferably performed with PCl5, prefera- be used as a heptazine source. bly at atmospheric pressure and using preferably phos- [0014] In one aspect of the invention the process for phoryl chloride POCl3 as reaction medium or solvent. obtaining cyameluric chloride (I) from cyameluric acid or The POCl3 is at the same time side product of the reaction 45 an alkaline salt of it is characterized in that cyameluric between the C6N7O3(R)3 and PCl5. acid or an alkaline salt of it is obtained from purified melon [0022] It can be recovered by distillation and it is con- powder. vertible into harmless and environmentally compatible [0015] It turned out to be favourable to remove produc- products by hydrolysis, which is contrary to alternative tion-determined existing melamine as well as other mo- solvents like high-boiling and chlorine containing aromat- lecular cyanamide derivatives, which are present as con- 50 ic solvents. taminants in the starting material (melon powder). [0023] In this invention the term "atmospheric pres- [0016] Different methods were successfully applied: sure" means pressures between 0.5 atm and 1.5 atm, calcinations at 560 °C under an inert atmosphere causes preferably 1 atm. condensation reactions of the low molecular weight con- [0024] Also in this invention the term "alkaline salt" taminants forming heptazine units, removal of volatile im- 55 means that R can be selected from sodium, potassium purities by evaporation/sublimation, and extraction or etc, preferably with complete substitution (three atoms) washing the polymeric starting material thoroughly with but includes any mixture wherein this substitution could water. not be complete.

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[0025] It was shown that cyameluric chloride is to be heterogeneous sublimate (with white and yellow colour) preferably sublimated in a sublimation apparatus with tu- has separated. The white material was identified as mela- bular geometry, as illustrated in figure 1, since in this mine by infrared spectroscopy. The weight of the ob- case substantially higher yields are obtained and, at the tained calcined melon was 86.8 g (yield 89 %), related same time, substantially pure products result. 5 to the pre-dried melon. The observed weight difference [0026] Very pure cyameluric chloride (I) is obtained by to the 93.2 g (m(raw melon) - m(sublimated material)) is due to fractioned vacuum sublimation in a tube-shaped, double the formation of ammonia (NH3) during the heat treat- walled (glass) set-up (figure 1). This apparatus consists ment (approximately 6.4 g were formed). The X-ray pow- of an outside vacuum tube (A) in which the inner (smaller) der diffraction pattern of the heat treated melon resem- tubes [(B1), (B2) and (B3)] are concentrically located. 10 bles the material reported in Komatsu (see Komatsu,T.; [0027] By the decreased heat flow at the axial contact Macromol. Chem. Phys.; (2001); 202; 19-25) which was surfaces of the tubes (see enlarged detail in figure 1) and designated as "orthorhombic melon". The overall yield by the radial isolation in relation to the environment due related to the assigned melon results thereby too 86.8 %. to the vacuum, a step-like temperature profile is formed. In consequence, the temperature difference within a sin- 15 1.2. Conditioning via Soxhlet-extraction with water. gle inner pipe is small, but significantly bigger between successive pieces (see enlarged detail in figure 1). [0033] Pelletized melon was milled into a fine powder. [0028] Therefore, the purified product deposits in the 64.4 g of this fine powder were placed in a Soxhlet-ex- inner pipe (B1) directly above the heating zone, while the traction set-up and extracted for 48 hours with distilled side products with high volatility deposit on (B2) and (B3) 20 water. The obtained aqueous solution was evaporated or are collected in one of the cooling traps. The first inner by means of a rotation evaporator, resulting in 5.1 g of a piece of pipe (B1) with the purified product may -after the white powder, which was analyzed to be melamine. The sublimation is finished- mechanically be separated from weigh of the purified melon which remained in the Soxh- the other pipes as well as the lower part of the glass set- let-extractor was determined after drying to be 57.5 g. up (C) which contains low or non-volatile impurities 25 The overall yield related to the assigned, non pre-dried and/or the raw material. The pure cyameluric chloride (I) melon results thereby to 89 %. can easily be collected without any contamination. [0029] If a sufficient pumping power is available, as 1.3. Conditioning via extraction with water. many sublimation tubes as desired can be operated in parallel at the same time. 30 [0034] 1 kg of pelletized melon was milled to a fine [0030] The following examples will further illustrate the powder, dispersed in 2 litres of distilled water and refluxed invention; they should not be interpreted as limiting the in a 4-litre flask. The hot mixture was filtered using a filter scope of the invention. nut and a vacuum pump. This procedure was repeated a second time with fresh distilled water. The overall yield Examples 35 related to the assigned, non pre-dried melon results to 925 g (yield 92%). Therefore, it is concluded that 2% of 1. Conditioning of the raw melon powder. melamine still remains in the purified product.

1.1. Conditioning by pyrolysis 2. Preparation of potassium cvamelurate. K3[C6N7O3] 40 [0031] 100 g pelletized melon was filed in a beaker and [0035] The synthesis and drying of the potassium stored for 48 hours in a drying oven at 120 °C. The weight cyamelurate from the purified and conditioned melon was of the obtained product was 97.4 g (that implies 2.8 % of performed in accordance with procedures known in the water in the starting material). The dried starting material state of the art (see Redemann,C.E.; J. Am. Chem. Soc.; was transferred to a quartz glass tube and evacuated 45 (1939); 61; 3420-3424). three times to ~ 10-1 mbar and flushed with dry argon. This pre-treated raw melon was then heated in the quartz 2.1. Preparation of cyameluric acid, H3[C6N7O3] glass pipe under an inert gas flow of nitrogen of approximately 10 I/h applying the following temperature pro- [0036] The synthesis of the cyameluric acid was per- gram: 50 formed in accordance with standard procedures known in the state of the art as it is by acidifying a solution of its a. heating from 20 °C to 120 °C in 30 minutes alkaline salt, previously obtained as indicated above. The b. maintain 120 °C during 4 hours acid, that has a very slow solubility in water, precipitates c. heating from 120 °C to 560 °C in 2 hours from the solution and can be separated by filtration. d. maintain 560 °C during 2 hours 55 3. Chlorination reaction Cooling by switching the heating off. [0032] In the colder zone of the quartz tube 4.2 g of a

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3.1. Chlorination of potassium cyamelurate with POCl3 carefully evacuated at room temperature. When the vac- as a reaction media uum was <10-2 mbar, the metal block (part (D) in figure 1) was heated to 50 °C. After 30 min. the temperature [0037] In a 1-litre two-necked flask equipped with reflux was increased to 150 °C and hold at this level fro 45 min. condenser and side stop-cock were placed 500 ml of 5 This procedure served for removing volatile contami- POCl3. Under flowing inert gas and stirring a powdered nants such as POCl3, PCl5 etc. mixture of 93.2 g (0.44 mmol) of PCl5 and 50 g (0.14 [0043] Afterwards, the temperature was increased to mmol) of dried potassium cyamelurate were added using 245 °C and hold for 6 h 30 min. During this period, the a powder funnel. The mixture was then refluxed for 4 h, vacuum reached from 4x10-3 to 6x10-3 mbar. The evac- whereby a bright yellow colour developed gradually. 10 uated sublimation tubes were cooled to room tempera- The POCl3 and the excessive PCl5 were removed by ture and transferred to a glove-box again. Purified distillation using a short glass tube connection instead of cyameluric chloride (I) was obtained as a bright yellow a distillation bridge (temperature of the oil bath was ap- layer with a thickness of up to 1 cm, which firmly sticks proximately 165 °C). The yellow residue in the flask was to the glass walls of tube B1. transferred into a glove-box with gas regeneration (≤0.5 15 [0044] The yield of one sublimation cycle was up to 20 ppm oxygen; ≤0.2 ppm water). After sublimation purified g (≈ 25% relative to raw melon powder from point 1.1). cyameluric chloride was obtained as described below.

3.2. Chlorination of cyameluric acid with POCl3 as a re- Claims action media 20 1. A process for obtaining cyameluric chloride (I) from [0038] In a 1-litre two-necked flask equipped with reflux cyameluric acid or an alkaline salt of it characterized condenser and side stop-cock were placed 500 ml of in that cyameluric acid or an alkaline salt of it is ob- POCl3. Under flowing inert gas and stirring a powdered tained from purified melon powder. 25 mixture of 100.0 g (0.472 mmol) of PCl5 and 31.0 g (0.14 mmol) of dried cyameluric acid were added using a pow- 2. The process according with claim 1 characterized der funnel. The mixture was then refluxed for 6 h, wherein that melon powder is purified by pyrolisis. by a vigorous reaction was observed and a yellow colour developed gradually. 3. The process according to claim 1 and 2 character- 30 The POCl3 and the excessive PCl5 were removed by ized in that the pyrolysis is carried out applying the distillation using a simple glass tube connection (temper- following temperature scheme: ature of the oil bath was approximately 160 °C). The yellow residue in the flask was transferred into a glove-box a. heating from room temperature to between with gas regeneration (≤0.5 ppm oxygen; ≤0.2 ppm wa- 100 °C and 200°C, preferably from room tem- ter). After sublimation (see below) less than 2 g of cyame- 35 perature to 120 °C in 60 minuts, preferably in 30 luric chloride was obtained as described below. minutes b. maintain between 100 °C and 200°C, prefer- 4. Purification of cyameluric chloride by vacuum frac- ably maintain 120 °C during at least 2 hours, tioned sublimation preferably during 4 hours 40 c. heating from between 100 °C and 200°C to [0039] 20 g of raw cyameluric chloride obtained as de- between 400 °C and 800°C, preferable from 120 scribed under section 3.1 were transferred in a glove-box °C to 560 °C in between 1 and 3 hours, prefer- to a glass tube labelled C in figure 1. This tube was placed ably in 2 hours into the (outer) sublimation tube shown in figure 1. The d. maintain between 400 °C and 800°C, prefer- other glass tube pieces (B1), (B2) and (B3) were then 45 ably maintain 560 °C during at least 1 hour, pref- also introduced into the (outer) sublimation tube. erably during 2 hours followed by cooling down. [0040] The purification of the raw cyameluric chloride was performed using four sublimation tubes of the type 4. The process according to claim 3 characterized in shown in figure 1 in parallel, i.e. at the same time. The that after pyrolysis temperature is cooled down be- latter four sublimation tubes were connected to a vacuum 50 low 50 °C, preferably until room temperature. system via a manifold. [0041] The vacuum system consisted of a two-stage 5. The process according to claim 1 characterized in rotary oil pump combined with an oil diffusion pump (max- that the melon powder is purified by extraction with imum end pressure ~ 10-6 mbar). The pressure during water, preferably at temperatures up to 80 °C. the sublimation was ~10-3 mbar. The pumps were pro- 55 tected against corrosive chemicals by two double-walled 6. The process according to claim 1 characterized in cooling traps and cooled with liquid nitrogen. that the melon powder is purified via Soxhlet-extrac- [0042] First, the argon filled sublimation tubes were tion with water at least during 24 hours, preferably

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during 48 hours. larged detail in figure 1) and by the radial isolation in relation to the environment due to the vacuum, a 7. The process according to claims 1 to 6 character- step-like temperature profile is formed. ized in that the main impurity eliminated is melamine. 5 16. The apparatus according with claims 13 to 15 characterized in that the temperature difference within 8. A process for obtaining cyameluric chloride (I) a single inner pipe is small, but significantly bigger between successive pieces (see enlarged detail in figure 1). 10 17. The apparatus according with claims 13 to 16 characterized in that the purified product deposits in the inner pipe (B1) directly above the heating zone, while the side products with high volatility deposit on (B2) 15 and (B3) or are collected in one of the cooling traps.

18. The apparatus according with claims 13 to 17 characterized in that first inner piece of pipe (B1) with the purified product may, after the sublimation is fin- 20 ished, mechanically be separated from the other pipes.

19. The apparatus according with claims 13 to 18 characterized in that the lower part of the glass set-up characterized by chlorination of cyameluric acid or 25 (C) which contains low or non-volatile impurities an alkaline salt of it with phosphorous pentachloride and/or the raw material may, after the sublimation is (PCl5) in phosphorous oxychloride (POCl3). finished, mechanically be separated from the other pipes. 9. The process according to claim 8 characterized in that the alkaline salt is preferably potassium cyame- 30 20. The apparatus according with claims 13 to 19 char- lurate. acterized in that depending on the pumping power available, as many sublimation tubes as desired can 10. The process according to claims 8 and 9 character- be operated in parallel at the same time. ized in that the chlorination reaction is performed under reflux conditions. 35 21. The process according with claim 13 wherein the vacuum fractioned sublimation steps are carried out 11. The process according to claims 8 to 10 character- with vacuum values from <10-2 mbar to 6x10-3 mbar ized in that the chlorination reaction is performed and temperatures from room temperature to 250 °C. at atmospheric pressure. 40 22. A process according with claims 8 to 12 for obtaining 12. The process according to claims 8 to 11 wherein the cyameluric chloride (I) by chlorination of cyameluric cyameluric acid or an alkaline salt of it is obtained acid or an alkaline salt of it, the cyameluric chloride from purified melon powder according to claims 1 to (I) obtained is purified by vacuum fractioned subli- 7. mation characterized in that the vacuum fractioned 45 sublimation is carried out through an apparatus ac- 13. A process for obtaining cyameluric chloride charac- cording with claims 13 to 21. terized in that the cyameluric chloride (I) is purified by vacuum fractioned sublimation through the appa- 23. A process according with claims 8 to 12 for obtaining ratus described in figure 1. cyameluric chloride (I) by chlorination of cyameluric 50 acid or an alkaline salt of it, characterized in that 14. The apparatus according with claim 13 character- cyameluric acid or an alkaline salt of it is obtained ized in that the outside vacuum tube (A) in which from purified melon powder according with claims 1 the inner (smaller) tubes [(B1), (B2) and (B3)] are to 7 and cyameluric chloride (I) is purified by vacuum concentrically located. fractioned sublimation carried out through an appa- 55 ratus according with claims 13 to 21. 15. The apparatus according with claims 13 and 14 characterized in that by the decreased heat flow at the axial contact surfaces of the tubes (see en-

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• US 3089875 A [0004] • DE 1102321 [0004] [0007] • US 3202659 A [0004] • DE 2106675 [0004] • US 2704716 A [0004] • US 4205167 A [0004] [0012] • US 2801172 A [0004]

Non-patent literature cited in the description

• MILLER,D.R. J. Am. Chem. Soc, 2004, vol. 126, • REDEMANN,C.E. J. Am. Chem. Soc., 1940, vol. 62, 5372-5373 [0002] 842-846 [0005] • XU, K. J. Am. Chem. Soc., 1994, vol. 116, 105 [0003] • SCHROEDER,H. J. Org. Chem., 1962, vol. 27, 4264 • KROKE,E. New J. Chem, 2002, vol. 26, 508-512 [0006] [0004] • KOMATSU,T. Macromol. Chem. Phys., 2001, vol. • PAULING,L. Proc. Nat. Acad. Sci. US, 1937, vol. 23, 202, 19-25 [0032] 615-620 [0004] • REDEMANN,C.E. J. Am. Chem. Soc., 1939, vol. 61, • FINKEL’SHTEIN,A.L. Russ. Chem. Rev., 1964, vol. 3420-3424 [0035] 33 (7), 400-405 [0004]