3
86ꢀ JOURNALꢀOFꢀCHEMICALꢀRESEARCHꢀ2009
N
X
N
N
R = methyl
R = ethyl
ROH/pyridine
Br
S
Br
R = octyl
∆
RO
S
OR
R = 2-propyl
R = 2-butyl
R= 2-pentyl
EtO
S
OEt
Br3
5
Br3
X = Br or H
Scheme 6ꢀ Proposedꢀin situꢀformationꢀofꢀdialkoxyphenothiazin-5-iumꢀsaltsꢀwithꢀalcoholsꢀ(seeꢀtextꢀforꢀcommentsꢀonꢀꢀ
theꢀstructure).
2
4
inꢀtheꢀformationꢀofꢀtetrabromophenol. ꢀInꢀtheꢀauthors’ꢀhandsꢀ
treatmentꢀofꢀphenothiazineꢀinꢀaceticꢀacidꢀwithꢀ2ꢀequivalentsꢀofꢀ
bromineꢀforꢀ30ꢀminꢀgaveꢀcompoundꢀ9ꢀandꢀtwoꢀuncharacterisedꢀ
redꢀ compoundsꢀ suggestingꢀ thatꢀ otherꢀ intermediatesꢀ orꢀ sideꢀ
reactionsꢀmayꢀbeꢀinvolved.
background reagent in the area of the fingerprint. The proposed
intermediatesꢀgeneratedꢀbyꢀreactingꢀsecondaryꢀalcoholsꢀwithꢀ
saltꢀ5,ꢀratherꢀthanꢀprimaryꢀalcohols,ꢀwillꢀbeꢀlessꢀpolarꢀbecauseꢀ
theꢀpolarꢀetherꢀgroupꢀisꢀmoreꢀhinderedꢀandꢀlessꢀavailableꢀtoꢀ
bindꢀ toꢀ aꢀ surface.ꢀThisꢀ mayꢀ allowꢀ moreꢀ readyꢀ diffusionꢀ onꢀ
aꢀ solidꢀ surfaceꢀ andꢀ enhanceꢀ theꢀ surfaceꢀ reactivity.ꢀ Chiralꢀ
alcoholsꢀwillꢀgiveꢀmixturesꢀofꢀracemicꢀandꢀmesoꢀproductsꢀandꢀ
soꢀhelpꢀtoꢀlowerꢀcrystallinityꢀandꢀfavourꢀdiffusion.
Theꢀ structureꢀ ofꢀ saltꢀ 5 was clarified this way. However,
purification by the literature method gave a product which
stillꢀ fumedꢀ whenꢀ theꢀ vialꢀ wasꢀ openedꢀ toꢀ theꢀ air.ꢀ Furtherꢀ
purification was achieved by stirring in acetonitrile for an
arbitrary period of 2 h, filtration and washing with acetonitrile
then ether. Its use for the development of latent fingerprints
wasꢀthenꢀinvestigated.
Summary
Latent fingerprints can be enhanced from a strong fingerprint
usingꢀ solutionsꢀ preparedꢀ byꢀ dissolvingꢀ 3,7-dibromo-
phenothiazin-5-iumꢀ perbromideꢀ inꢀ secondaryꢀ alcohols.ꢀ Theꢀ
fingerprints show good light fastness. The image quality
isꢀ howeverꢀ reducedꢀ byꢀ blotches.ꢀ Theꢀ reagentꢀ isꢀ aꢀ polarꢀ
saltꢀ withꢀ aꢀ largeꢀ surfaceꢀ areaꢀ soꢀ willꢀ absorbꢀ stronglyꢀ ontoꢀ
surfacesꢀ reducingꢀ itsꢀ reactivityꢀ andꢀ preventingꢀ diffusion.ꢀ
Theꢀbackgroundꢀcolourationꢀofꢀtheꢀreagentꢀisꢀpartlyꢀquenchedꢀinꢀ
the fingerprint region so the enhancement of latent fingerprints
isꢀ notꢀ solelyꢀ dueꢀ toꢀ displacementꢀ ofꢀ alkoxyꢀ substituentsꢀ
fromꢀtheꢀproposedꢀintermediateꢀsalts.ꢀEvidenceꢀisꢀpresentedꢀ
helpingꢀ toꢀ characteriseꢀ theꢀ 3,7-dibromophenothiazin-5-iumꢀ
salt. Treatment with cyclohexene or sodium sulfite gives 3,7-
dibromophenothiazine.
Latent fingerprints
Toꢀ formulateꢀ saltꢀ 5ꢀ aꢀ smallꢀ quantityꢀ (~ꢀ 25–50ꢀ mg)ꢀ wasꢀ
dissolvedꢀ inꢀ differentꢀ alcoholsꢀ (100ꢀ mL)ꢀ byꢀ heatingꢀ withꢀ
anꢀ excessꢀ ofꢀ pyridineꢀ (0.5ꢀ mL).ꢀ Withoutꢀ anyꢀ pyridineꢀ
dissolutionꢀ wasꢀ muchꢀ slowerꢀ suggestingꢀ thatꢀ theꢀ baseꢀ
assistedꢀtheꢀnucleophilicꢀdisplacementꢀofꢀtheꢀbromineꢀatomsꢀ
byꢀ theꢀ alcohol.ꢀ Theꢀ solutionsꢀ wereꢀ initiallyꢀ darkꢀ greenꢀ butꢀ
over 2 days a fine precipitate settled leaving a red solution.
Henceꢀ3,7-dialkoxyphenothiazin-5-iumꢀsaltsꢀareꢀproposedꢀasꢀ
intermediatesꢀgeneratedꢀin situꢀbutꢀhaveꢀnotꢀbeenꢀcharacterisedꢀ
anyꢀ furtherꢀ (Schemeꢀ 6).ꢀ The in situꢀ generationꢀ ofꢀ 3,7-
diethoxyphenothiazin-5-iumꢀbromideꢀinꢀethanolꢀfromꢀsaltꢀ5ꢀhasꢀ
beenꢀstudiedꢀpreviously. ꢀItꢀwasꢀreportedꢀasꢀaꢀcherryꢀredꢀsaltꢀ
but it was purified by chromatography on silica gel (Rf = 0.8ꢀ
withꢀCHCl ).ꢀThisꢀisꢀratherꢀnon-polarꢀforꢀaꢀbromideꢀsaltꢀsoꢀ
weꢀproposeꢀthatꢀtheꢀcompoundꢀisꢀaꢀneutralꢀadductꢀ(Schemeꢀ6)ꢀ
withꢀ(Xꢀ=ꢀBr)ꢀorꢀtheꢀreducedꢀformꢀ(Xꢀ=ꢀH).ꢀItꢀwasꢀprepared ꢀ
byꢀpurgingꢀanꢀethanolicꢀsolutionꢀofꢀsaltꢀ5ꢀwithꢀnitrogenꢀforꢀ
4ꢀ hꢀ whichꢀ mightꢀ driveꢀ offꢀ liberatedꢀ bromineꢀ shiftingꢀ theꢀ
equilibriumꢀ structureꢀ ofꢀ theꢀ counterionꢀ fromꢀ perbromideꢀ toꢀ
bromide.ꢀTLCꢀofꢀaꢀmethanolicꢀsolutionꢀofꢀsaltꢀ5ꢀafterꢀheatingꢀ
withꢀaꢀsmallꢀquantityꢀofꢀpyridineꢀandꢀstandingꢀforꢀ24ꢀh,ꢀduringꢀ
whichꢀtimeꢀtheꢀsolutionꢀturnedꢀfromꢀgreenꢀtoꢀred,ꢀshowedꢀaꢀ
redꢀ productꢀ whichꢀ elutedꢀ readilyꢀ withꢀ etherꢀ butꢀ alsoꢀ muchꢀ
colouredꢀdyeꢀonꢀtheꢀbaseline.
A strong fingerprint was prepared on a silica sheet by
pressingꢀaꢀdampꢀthumbꢀontoꢀit.ꢀThisꢀwasꢀdippedꢀonceꢀintoꢀtheꢀ
dipꢀsolutionꢀthenꢀdriedꢀforꢀupꢀtoꢀ5–10ꢀminutesꢀinꢀanꢀovenꢀatꢀ
15
Experimental
IRꢀ spectraꢀ wereꢀ recordedꢀ onꢀ anꢀ ATIꢀ Mattsonꢀ FTIRꢀ spectrometerꢀ
3
usingꢀ KBrꢀ discs.ꢀ UVꢀ spectraꢀ wereꢀ recordedꢀ usingꢀ aꢀ Perkin-Elmerꢀ
1
Lambdaꢀ 25ꢀ UV-VISꢀ spectrometerꢀ withꢀ CH Cl ꢀ asꢀ theꢀ solvent.ꢀ Hꢀ
15
2
2
1
3
andꢀ CꢀNMRꢀspectraꢀwereꢀrecordedꢀatꢀ400ꢀMHzꢀandꢀ100.5ꢀMHzꢀ
respectivelyꢀusingꢀaꢀVarianꢀ400ꢀspectrometer.ꢀ CꢀNMRꢀDEPTꢀ135ꢀ
13
2
wasꢀusedꢀtoꢀdistinguishꢀquaternaryꢀcarbonsꢀfromꢀCHꢀcarbons.ꢀLowꢀ
resolutionꢀ massꢀ spectraꢀ wereꢀ obtainedꢀ atꢀ theꢀ Universityꢀ ofꢀ Wales,ꢀ
Swanseaꢀ usingꢀ EI,ꢀ CIꢀ andꢀ ESꢀ ionisationꢀ methods.ꢀAccurateꢀ massꢀ
spectraꢀwereꢀdeterminedꢀatꢀtheꢀUniversityꢀofꢀWales,ꢀSwanseaꢀusingꢀ
ES ionisation methods. Melting points were determined on a Kofler
hot-stageꢀmicroscope.ꢀ3,7-Dibromophenothiazin-5-iumꢀperbromideꢀ5
15
was prepared following the literature method with one modification. ꢀ
Purification was achieved by stirring the red salt in acetonitrile for 2
h then filtration and washing with acetonitrile then ether. Solutions
for the enhancement of latent fingerprints are described in the text
withꢀfullꢀdetails.
3
,7-Dibromophenothiazine (9):ꢀ Intensityꢀ dataꢀ forꢀ aꢀ paleꢀ greenꢀ
prismꢀofꢀ1ꢀwereꢀcollectedꢀonꢀaꢀNoniusꢀKappaꢀCCDꢀdiffractometerꢀ
MoKaꢀ radiation,ꢀ lꢀ =ꢀ 0.71073ꢀ Å)ꢀ atꢀ Tꢀ =ꢀ 120ꢀ K.ꢀ Theꢀ structureꢀ
1
00ꢀ°C.ꢀFingerprintsꢀdippedꢀintoꢀmethanol,ꢀethanolꢀorꢀoctanolꢀ
dipsꢀ gaveꢀ veryꢀ poorꢀ imagesꢀ thatꢀ hadꢀ noꢀ detailꢀ ofꢀ linesꢀ orꢀ
ridges.ꢀ Fingerprintsꢀ dippedꢀ intoꢀ isopropanol,ꢀ 2-butanol,ꢀ orꢀ
(
was solved by direct methods with SHELXS-97 and refined
usingꢀSHELXL-97.ꢀTheꢀN-boundꢀhydrogenꢀatomꢀwasꢀlocatedꢀinꢀaꢀ
difference map and its position was freely refined; the C-bound
hydrogen atoms were geometrically placed and refined as riding.
Crystalꢀ data:ꢀ C H Br NS,ꢀ M ꢀ =ꢀ 357.07,ꢀ orthorhombic,ꢀ Pnmaꢀ
2
-pentanolꢀsolutionsꢀofꢀreagentꢀ5ꢀdevelopedꢀimagesꢀdisplayingꢀ
linesꢀandꢀridges.ꢀThisꢀobservationꢀofꢀtheꢀneedꢀforꢀsecondaryꢀ
overꢀ primaryꢀ alcoholsꢀ supportsꢀ theꢀ viewꢀ thatꢀ theꢀ alcoholsꢀ
haveꢀ reactedꢀ withꢀ saltꢀ 5.ꢀ 2-Butanolꢀ wasꢀ theꢀ bestꢀ solvent.ꢀ
Theꢀlinesꢀareꢀpinkꢀorꢀpaleꢀredꢀandꢀwereꢀobservedꢀinꢀvisibleꢀ
light.ꢀHeatingꢀaꢀgreenꢀmethanolꢀdipꢀofꢀsaltꢀ5ꢀwithꢀaꢀsuspensionꢀ
ofꢀglycineꢀforꢀaꢀfewꢀminutesꢀgivesꢀaꢀredꢀsolutionꢀ(ratherꢀthanꢀ
theꢀcolourꢀofꢀmethyleneꢀblue)ꢀwhichꢀexplainsꢀtheꢀcolourꢀofꢀ
the developed fingerprints. The dips will develop fingerprints
afterꢀmanyꢀweeks.
The fingerprints showed good light stability without fading
inꢀ ambientꢀ daylightꢀ afterꢀ oneꢀ week.ꢀ Theꢀ imageꢀ qualityꢀ isꢀ
howeverꢀ reducedꢀ inꢀ someꢀ regionsꢀ byꢀ pinkꢀ blotches.ꢀ Theꢀ
visibility of the fingerprint is enhanced by bleaching of the
1
2
7
2
r
(
No.ꢀ62),ꢀZꢀ=ꢀ4,ꢀaꢀ=ꢀ7.7968ꢀ(2)ꢀÅ,ꢀbꢀ=ꢀ24.3333ꢀ(6)ꢀÅ,ꢀcꢀ=ꢀ5.9341ꢀ(1)ꢀÅ,ꢀ
3
–3
–1
Vꢀ=ꢀ1125.83ꢀ(4)ꢀÅ ,ꢀF(000)ꢀ=ꢀ688,ꢀrꢀ=ꢀ2.107ꢀgꢀcm ,ꢀmꢀ=ꢀ7.35ꢀmm ,ꢀ
–3
min.,ꢀmax.ꢀDrꢀ=ꢀ–0.52,ꢀ+ꢀ0.46ꢀeꢀÅ , R(F) = 0.029 (1160 reflections),
2
wR(F ) = 0.069 (1324 reflections). CCDC 732813
3,7-Dibromo-10H-phenothiazine (9):ꢀ Compoundꢀ 5ꢀ (330ꢀ mg,ꢀ
.554ꢀmmol )ꢀwasꢀstirredꢀinꢀacetonitrileꢀwithꢀanꢀexcessꢀ(1ꢀmL)ꢀofꢀ
-1
0
cyclohexeneꢀforꢀ16h.ꢀTheꢀreactionꢀwasꢀdilutedꢀwithꢀwaterꢀformingꢀ
a precipitate. This was collected by filtration, washed with water
thenꢀmethanol.ꢀTheꢀgreenꢀsolidꢀwasꢀdissolvedꢀinꢀCH Cl and filtered
2
2
through a pad of flash silica, concentrated in vacuoꢀandꢀdriedꢀoverꢀ
calciumꢀchlorideꢀtoꢀgiveꢀtheꢀtitle compoundꢀ(95ꢀmg,ꢀ40%)ꢀasꢀaꢀyellowꢀ
1
9
solidꢀm.p.ꢀ210–212ꢀ°Cꢀ(lit.ꢀ206–209ꢀ°C) ꢀ(Found:ꢀC,ꢀ40.5;ꢀH,ꢀ1.9;ꢀN,ꢀ
Plater, John
