CEJC 1(2003)53{64 1,3-bis(2,4,6-trinitrophenylaminooxy)propane andits 4-cyano-2,6-dinitrophenylCongener: Synthesisand Prop erties. Irina C. Covaci 1,PetreIonita 1,MironT. Caproiu 2,RaduSocoteanu 1, Titus Constantinescu 1,AlexandruT. Balaban 3;4 1 RoumanianA cademy,Institute ofPhysical Chemistry \I.G.Murgulescu", Laboratoryof Supramolecular Chemistry and Interphase Processes, SplaiulIndependentei 202, 77408, Bucharest, Roumania 2 RoumanianA cademy,Institute \C.D. Nenitzescu" ofOrganic Chemistry, SplaiulIndependentei 202B, 77408, Bucharest, Roumania 3 University \Polytechnica",Faculty of Industrial Chemistry, Departmentof Organic Chemistry, Bucharest, Roumania 4 TexasA&M University atGalveston, Galveston,TX 77553-1675,USA Received 4October 2002;revised 24December 2002 Abstract: Starting fromN-hydroxyphthalimide (5) and1,3-dibromopropane (6) weobtained 1,3-bis(phthalimidooxy)propane (7) which led to 1,3-bis(aminooxy)propane dihydrochloride (8). Fromits reaction with picryl chloride or4-cyano-2,6-dinitrochlorobenzene, the twotitle compounds(4b, 4a)were obtained. 1H-NMR and 13C-NMRspectra arepresented. Forcomparisonwith the analogousN-methoxy- 2,6-dinitro-4-R-anilines 1a,1b (R=CNorR=NO 2), wereport the hydrophobic characteristics (by RPTLC), electronic spectra for the neutral compoundsand their anions, pK a values, andthe behavior towardsoxidizers (DPPH, PbO 2;Pb(CH3COO)4, KMnO4 and Ag2O); DPPH converts compounds1a, 1b and 4a, 4b into betainic structures 2a,2b respectively. c Central EuropeanScience Journals. All rights reserved. ® Keywords:N-alkoxyaryl derivatives; RPTLC; pK a;NMR;oxidation 1Introduction It was shown in previous papers [1- 10]that compounds of type 1present interesting properties when substituents are strong electron acceptors (e.g.1a, 1b). Among these properties, the generation of N-alkoxyaminylfree radicals on oxidation [4- 8]allowed a 54 A.T.Balaban et al. / CentralEuropean Journal of Chemistry 1(2003)53{64 reaction with the free stable radical DPPH (2,2-diphenyl-1-picrylhydrazyl) leading to be- tainicstructures 2a,2b, which can bereduced reversiblyto the corresponding hydrazines 3a,3b [1,9,10].Basic media lead to the formation ofthe corresponding anions with colors that depend on the substitution pattern [1,2]. Continuing our research, we investigated the possibility to obtain new compounds of Ar-NH-O-(CH 2)n-O-NH-Ar type and to study their properties comparativelyto their analogous compounds of type 1.F or this purpose we synthesized the new compounds 1,3-bis(4-cyano-2,6-dinitrophenyloxy)propane (4a) and 1,3-bis(picramidooxy)propane or 1,3-bis(2,4,6-trinitrophenylaminooxy)propane (4b), and investigated their properties com- parativelywith those ofcompounds 1a,1b [2]. 2Resultsand Discussion 2.1 Synthesis of compounds 4a, 4b Compounds 4a,4b were synthesized in three-steps [1,2,5,11,12]:(i) in the ¯rst step, N-hydroxyphthalimide 5and 1,3-dibromopropane 6ledto 1,3-bis(phthalimidooxy)propane, 7(yield79%); (ii) in the second step, acidhydrolysis ofcompound 7gave A.T.Balaban et al. / CentralEuropean Journal of Chemistry 1(2003)53{64 55 1,3-bis(aminooxy)propane dihydrochloride, 8(yield40%); (iii) ¯nally,compounds 4a,4b were obtained from the reaction of compound 8with 4-cyano-2,6-dinitrochlorobenzene, 9a,or with 2,4,6-trinitrochlorobenzene (picryl chloride) 9b (yields88.5% and 72%,re- spectively). Fig. 1 Synthesis of compounds4a,b The structures of the new 4a,b compounds were con¯rmed by 1H- and 13C- NMR (Table1), elementalanalysis, and their physico-chemicalproperties. Comp. 1H-NMR 13C-NMR 4a 11.30(b, N-H, deuterable); 138.50(C-1); 136.18(C-2-6); 8.67(s, 2H, H-3-5); 133.82(C-3 or C-5); 3.88(t, 4H, H- ¬ , 6.6); 133.71(C-5 or C-3); 116.31(C-4); 1.93(quintet, 2H, H- ­ , 6.6). 99.02(CN); 72.72(C- ¬ ); 25.40 (C- ­ ). 4b 11.30(b, N-H, deuterable); 139.24(C-1);134.58 (C-2-6); 8.81(s, 2H, H-3-5); 133.46(C-4); 125.49(C-3-5); 3.94(t, 4H, H- ¬ , 6.7); 72.77 (C- ¬ ); 25.75 (C- ­ ). 1.74(quintet, 2H, H- ­ , 6.7). 7 7.84(b, 4H, H-3-6); 163.41(CO);134.80 (C-3-6); 4.36(t, 4H, H- ¬ , 5.2); 128.60(C-1-2); 123.25(C-4-5); 2.09(quintet, 2H, H- ­ , 5.2). 74.42 (C- ¬ ); 27.11 (C- ­ ). 8 11.40(s, N-H, deuterable); 70.73 (C- ¬ ); 26.03 (C- ­ ). 4.08(t, 4H, H- ¬ , 5.4); 1.93(quintet, 2H, H- ­ , 5.4). Table 1 NMR spectraof compounds4a,b, 7 and8 inDMSO-d 6: ¯ values,ppm; J (Hz) 56 A.T.Balaban et al. / CentralEuropean Journal of Chemistry 1(2003)53{64 2.2 Propertiesof compounds 4a, 4b (a) Electronic absorption spectra Electronic absorption maximaof the new compounds 4a,b are presented inTables2 and 3. Compound: 4a 4b Solvent, ET (30)¤ ¶ max nm, (log ") ¶ max nm, (log ") CH2Cl2 (41.1) 398 (3.48) 338 (4.33) Acetone (42. 2) 573 (2.94) 450 (3.79) DMSO-d6(45.0) 400(3.96) and579 (3.72) 384(3.96) and498 (4.00) H3COH (55.5) 396(2.72) and570 (2.95) 356(4.29) and460 (4.31) Table 2 UV-VIS spectraof compounds4a,b; ¤ Dimroth-Reichardtparameters [13] The UV-Vis spectra (Table2) provide the evidenceof the in°uence of solvent polarity measured by the Dimroth-Reichardt parameters [13];a slight bathocromic shift isobserved as the E T (30) valueincreases (positive solvatochromic e®ect). The caseof methanol isan exceptionbecause it isa protic solvent. The electronicspectra of the anions of compounds 4a,b are presented in Ta- ble3; these larger shifts account for the blue colorof the anion of compound 4a (¶ max =580 nm) and the red colorfor that ofcompound 4b ( ¶ max = 530 nm). Compound ¶ max, nm, (log ") Color 4a 416(3.52) and580 (3.74) blue 4b 384(3.52) and530 (3.74) red Table 3 Visibleabsorption spectra of the anionsof compounds4a,b* *InDMSO +KOH (the molarratio compound : KOH =1: 2) The electronicspectra of the new compounds 4a,b (Table3) are similarto those of their analogs 1a,b (Table4) [2,14].Some di®erences exist between the anion of compound 4b (table 4)and the anion of compound 1b(Table4). (b) Acidity Our previous papers [1,2]showed that compounds of type 1exhibit acidiccharacter- isticsdepending on the nature and the position of the substituents [2].Among the compounds 1previouslystudied [1,2],the compounds two nitro groups and one car- boxygroup were the onlyones with two ionizableprotons due to the COOHgroup (pKa1)and to the NH-OMegroup (pK a2).The compounds 4a,b were synthesized in order to investigatea di®erent kind of bis-acidicspecies due to the two NH-OR groups contained in the molecule.T able6 shows the pK a values(determined by A.T.Balaban et al. / CentralEuropean Journal of Chemistry 1(2003)53{64 57 Comp. Neutral compound Anion a b;c b;c ¶ max,nm (log ") ¶ max,nm (log ") Color 1a 270(4.27); 399(3.56) 400(3.94); 583(3.73) blue 1b 333(4.32); 402(shoulder) 462(4.21); 600(shoulder) red Table 4 Electronicabsorption maxima of compounds1a,b and their anions [2,14]. a In dichloromethane; b indichloromethane as supramolecular complex with the crownether 18-crown-6 and KOH for1a [2]; c inmethanol-water with NaOH (1: 1,v/ v) molarratio 1 :1compound: NaOH [14]. potentiometric titration) of compounds 4a,b and 1a,b [1,2]. Comp. pKa Comp. pKa1 pKa2 1a 7.54 4a 5.05 8.55 1b 5.00 4b 4.00 8.21 Table 5 The pKavaluesof compounds4a,b and 1a,b The data from Table5 show that indeed compounds 4a,b exhibit two ionization steps, di®ering by 3-4 orders of magnitude. The higher acidityof compounds 4 relativelyto compounds 1maybe due to asupplementary intramolecular hydrogen bonding between an oxygenatom and an NHgroup from the bis(aminooxypropane) group, thus depressing the electron density around that oxygen.The lower acidityof a-type compounds relativelyto b-type compounds isdue to the CNgroup from the para position, which has alower electron-withdrawing e®ect than the NO 2 group. Taking into account the colors of these anions that facilitatethe visualizationof the acid-base reaction (similarlyto compounds oftype 1) [15],the new compounds 4can beused analyticallyfor the extraction of alkalinecations or amino acidsin the presence ofacrown ether [16]. (c) Solubility and hydrophobicity Compounds 4a,b havelow solubilityin water. Compound 4a isalso less soluble in most organic solvents,whereas compound 4b ishighly soluble in organic solvents. This leads to aslight di®erence from compound 1a which isless soluble in water but highly soluble in organic solvents [1,2].The retention factors R f ofcompounds 4a,b and 1a,b in aliquid/liquidsystem depend onthe acidityof the aqueous phase. Table6 shows the results obtained using reversephase thin layerchromatographs (RPTLC). There isa linear correlation between logR f and the pH of the aqueous phase, asindicated by the correlation coe±cient ( r 0.90) for the equation indicated ¶ under Table6. As the concentration of the acidicphase decreases,the compounds willbegin to be found as the corresponding anions that are soluble in aqueous phase, therefore the Rf valueswill increase. A supplementary argument isthat at hydrochloric acid 58 A.T.Balaban et al. / CentralEuropean Journal of Chemistry 1(2003)53{64 Comp. 1M0.1M 0.01M 0.001M 0.0001M r # 1a 0.480.48 0.50 0.60 0.61 0.90 1b 0.300.31 0.54 0.73 0.77 0.95 4a 0.300.34 0.34 0.45 0.47 0.95 4b 0.160.17 0.20 0.68 0.73 0.91 Table 6 Rf valuesof compounds1a,b and 4a, b atv ariousacidities ¤ ¤ RPTLC platesMerck RP-18F 254s; mobilephases ethanol / hydrochloricaqueous acid (1M.