Page 29 - BRAVO-3 | ISSUE 2 | JULY/AUGUST 2018

AfterdeterminingtherateofHMTDdecompositioninacetonitrilealone,additionalanalytes,includingwater, acidsandbases,wereaddedandthedecompositionratesmonitoredwithtime.Headspacesamplingresults indicatethatwater,intheform ofhumidity,afectstherateofformationforseveraldecompositionspecies presentwithintheheadspace.WaterwasaddedatvariouslevelstoHMTD solutions(Figure2&Table3). With1% addedwater,adiferencenotexceedingthe7% erordeterminedfortherateconstants,was observed.At4.8% and9.1% ofwateradded,ameasuredaccelerationintherateofHMTDdecomposition wasobserved.
Inadditiontowater,decompositionofHMTD inthepresenceofacidsandbaseswasobserved.Both hydrochloricacid(HCl)andcitricacidhavebeenusedascatalystsinHMTD syntheticprocesses.These acids,inadditiontoformicacidwhichdominatestheHMTD headspace,wereinvestigatedtodetermine whetheroneofthesespeciescouldinitiateanddrivethedecompositionprocess.Theefectofbases,sodium hydroxide(NaOH)andtrimethylamine(TMA),werealsoassessedforcomparisonpurposes(Table3).The additionofHClresultedinHMTDdecompositionataratetoorapidtobedetermined,evenwhenheldat0°C.
Halsoresultedinarapid,thoughmeasureable,rateofdecomposition.Addingformicacidintheabsence ofwaterreducedthehalf-lifeto330hoursat50°C,onlyamodestreductionfrom 408hoursat50°C withno addedacid;however,whentheformicacidwasaddedinadditionto4.8wt% water,thehalf-lifewasreduced to83hours.Thiswaslikelyduetotheenhanceddissociationoftheweakacidinsolutionwiththeadded water.Likewise,anaqueoussolutionofcitricacidwasadded,decreasingthehalf-lifetojust3.1hours.Solid citricacidwaspoorlysolubleinacetonitrile,and,thus,theefectofanhydrouscitricacidcouldnotbe
N
N
a
a
O
OH
daswaspossiblewithformicacid.Similarly,addingtrimethylamineasasolutioninethanol,withno additionalwater,reducedthehalf-lifeofdecompositionfrom 408hoursat50°C to27hours.
TheefectofacidsonthedecompositionofHMTDwasquiteprofound.Thepresenceofcopiousamounts offormicacidformedduringtheheadspacemonitoringexperimentsaswelasheobservedsensitivityto w a te r fro m h u m id ifie d a ir (T a b le 2 ) a re lik e ly to e x a c e rb a te H M T D d e c o m p o s itio n . T rim e th y la m in e h a s a ls o beenobservedintheheadspace,althoughinmuchlowerquantities,andisthusnotlikelytocontribute significantlytothedecompositionofHMTD.
c
c
o
om
mp
p
a
ar
re
e
d
WWW.BRAVO-3.COM
29