Notes Bull. Korean Chem. Soc. 2009, Vol. 30, No. 12 3105 DOI10.5012/bkcs.2009.30.12.3105
Synthesis of Phloroglucinol Using Microwave-Assisted Reaction from TNT
Woong HeeLee,JinSeukKim： andSeok Chan Kim*
Department ofBio&Nano Chemistry, Kookmin University, Seoul 136-702, Korea. *E-mail: [email protected]
^Agency forDefense Development,P. O. Box 35-5, Yuseong, Daejeon 305-600,Korea Received September 14, 2009, Accepted October 19, 2009
KeyWords: TNT,Microwave-assistedreaction,Phloroglucinol,Resorcinol
Millions of poundsofsurplusenergeticmaterials such as TNT, DNTandammonium picrate havebeen disposed by open burning/detonation.1 Theuse of open burning/detonation is be comingunacceptable due topublic concern andenvironmental regulations.Therefore,the chemical conversion study of surplus energeticmaterialsto highervalue products would behighly desirable.The commercial conversion methods to Phlorogluci nol (4) which isusedin the pharmaceutical,cosmetics, textile
dying and photographic industries from TNTwere developed.2 However, this conventional synthesiswasnolonger used be
cause of mainly environmentalproblems associated with waste disposal (Scheme 1).3
Recently, microwaveassisted reactionhas become a powerful toolin organicsynthesis,which is beingincreasinglyused to accelerate theorganicreactions. Microwave assisted organic reactions have a remarkable meritsof increased yields, reduced reaction time,suppressed side products anddecreased environ mental pollution.4-6 Thus, use of microwaveirradiation inor
ganicsynthesis has become a powerfulmethod for the rapid synthesis ofa variety oforganic molecules with improvedyield.
Here,wewish to report moreeco-friendlysynthetic proce
dure focusingon microwave-assistedreaction for the synthesis ofPhloroglucinol (4) from TNT.First,TNT(1) is oxidized to 2,4,6-trinitrobenzoicacid and thermallydecarboxylated to 1, 3,5-trinitrobenzene (2) in two steps 85%yield.3 Subsequent reduction of 2 with hydrazine and Fe/C7 delivered 1,3,5-tria- minobenzene(3)in95% yield. Hydrolysis of 3in largeexcess of HClsolutionat110 oC for 24 hours producedPhloroglucinol (4) in only50% yield alongwith unidentified side products. This results are consistentwiththefact that aromatic substitution reaction with poorleavinggroupsby nucleophile proceedsvery slowly with low yield.8 Ontheother hands, when this reaction was run under microwaveirradiation,the reaction proceeded rapidly.Different experimental conditions have been testedon 3 and 5 tofind the best results. The best conditionto occur reac tion under microwave heatingis that theobserved temperature was 180 oC after 30 sec heating at 400 W andirradiation was
continued for 15 min at thesame power.The reaction rateand yields were significantly enhancedby microwave irradiation (Table 1).Therate enhancementundermicrowaveirradiation maybeattributedto theabsorption of more microwaveenergy, which generates sufficient heatenergyto promote the reaction.
Phloroglucinol (4)andresorcinol (6) from TNT and DNT were rapidly obtained comparedwith thereaction underconventional heating (entries1 and 2).Moreover, it was foundthat only 1.5 equivalent of HCl solution was sufficientto induce nucleophilic substitution reaction.
Wehaveextended our study to thereactionsof7 and 9 with same conditions as shown in Scheme2 toinvestigatesubstitu tion effect bychangingfromhydrogentomethylgroup.Thus, TNTandDNT was directlyreduced andreactedwithHCl solu tion undermicrowave irradiation to afford the products8 and 10 (entries3 and 4). These results show that increased inductive effectbymethylgrouponthe benzene ringhas no significant differenceunder microwaveassistedorganicreaction.
In summary, we have preparedsome hydroxy aromatic com pounds in good yieldsusing microwave irradiation.Main advan tages of thisarticle isthat nucleophilicsubstitution reaction of aromaticcompound with poorleaving group proceeded much morequickly andwithhigher yields under microwave irradiation thanconventionalheating.The future work includingapplica tion of microwaveirradiation to biologically active compound is under investigation in our laboratory.
3, Ri = NH2, R2= H 5, Ri = H, R2 = H 7, Ri = NH2, R2 = CH3
9, Ri = H, R2 = CH3
Microwave aq. HCI
4, Ri = OH, R2= H 6, Ri = H, R2 = H 8, Ri = OH, R2 = CH3
10, Ri = H, R2 = CH3
Scheme 2
1) Ox.
2) △
O2N
NO2
2
NO2 Re. 5
3
aq. HCI HO、尸YOH
OH 4 Scheme 1. Commercial Product of Phloroglucinol (4) from TNT (1)
3106 Bull.KoreanChem. Soc. 2009, Vol. 30, No. 12 Notes Table 1. Conversion of 3, 5, 7 and 9 to 4, 6, 8 and 10 promoted by
microwave.
Entry Starting
Material Producta Time
(min)‘ Temp (oC) Yield (%)c
150 61
10 180 70
210 82
150 65
1 3 4 15 180 85
210 85
150 79
30 180 84
210 85
150 59
10 180 68
210 78
150 62
2 5 6 15 180 82
210 82
150 73
30 180 81
210 82
150 72
10 180 78
210 84
150 81
3 7 8 15 180 90
210 89
150 85
30 180 89
210 90
150 68
10 180 75
210 82
150 78
4 9 10 15 180 86
210 86
150 81
30 180 85
210 86
aAll productswere characterized by 1HNMR and FT-IR.‘Microwave irra
diation wascarried out at 400 Watts using Initiator microwave oven. cYield refers topure productsafter chromatography or recrystallization.
ExperimentalSection
General. All proton nuclearmagnetic resonance (NMR) spec tra wererecorded on a VarianUnityInova spectrometerat300 MHz and are reported in parts per million(ppm)onthe8scale relative to chloroform-* or DMSO-必.IR spectra were recorded
ona Varian FT-IR spectrometer using KBroptics. Analytical thin layerchromatography (TLC)was performedwith E.Merck pre-coatedTLCplates,silicagel60F-254,layerthickness 0.25 mm. Column chromatography was donewith silica gel 60 (70 - 230 mesh ASTM) from E. Merck mostly bygravity.Initiator 400 Wmicrowave oven was used toperformthereaction.
Phloroglucinol (4):The solution of 1,3,5-triaminobenzene (3, 1.0 g, 8.85 mmol), 36% HCl (4.0 g, 40.0mmol, 1.5 eq.) and H2O(10.0mL) was placedintomicrowave oven at180 oC and irradiated for the periodlisted in Table1.The reactionmix ture was extractedwithethyl acetate(3 乂 5 mL). The combined organiclayers weredried over anhydrous MgSO4 and solvent was removed underreduced pressure to obtain the crude product.
Pure product wasobtained byrecrystallization with ether and methanol as white solid (0.93 g, 95%).m.p.217 〜220 oC; 1H NMR(300 MHz, DMDO-必)8 9.0 (s, 3H), 5.64 (s, 3H); IR (KBr)Umax 3430, 1620,1490 cm-1.
Resorcinol(6): m.p. 109 〜111 oC; 1H NMR (300 MHz, DMDO-必)8 9.15 (s, 2H),6.93 (dd, J= 8.2, 8.1 Hz, 1H), 6.21 (m, 3H); IR(KBr)喝必 3240, 1610, 1490 cm-1.
2,4,6-Tiihydioxytoluene(8):m.p. 213 〜219 oC; 1H NMR (300MHz,DMDO-必)88.81 (s, 2H),8.68 (s, 1H),5.84 (s, 2H), 1.92(s, 3H);IR (KBr)Umax 3230, 1630, 1470cm-1.
2,4-Dihydroxytoluene (10): m.p. 105 〜106 oC; 1H NMR (300MHz, DMDO-必)8 8.89(br,2H),6.84(d, J= 8.8Hz, 1H), 6.28 (d, J = 2.0 Hz, 1H), 6.20 (dd, J= 8.8, 2.0 Hz,1H), 2.05 (s, 3H);IR (KBr)喝必 3330, 1620,1480 cm-1.
Acknowledgments. This research was supported by the KookminUniversityResearch fundand alsosupported by Ko rean Agency for DefenseDevelopment.
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