Acylation of Ferrocene
Harold T. McKone St. Joseph College West Haftlord. CT 06117
Effect of temperature on reactivity as measured by reverse phase high performance liquid chromatography
T h e Friedel-Crafts Reaction. a widelv used svnthetic tool. is a n integral part of most organic laboratory courses. Formallv. benzene was the preferred substrate for this electrophili"c'suhstitution reaction. However, recent reports confirming benzene's carcinogenicity necessitate using a safer aromatic compound. Ferrocene (I)is a reasonable alternative since it is relatively non-toxic, stable, more reactive than brnzenc, inexpensive in the quantities needed per student, and affords a n intrrrsting array of acylafion products (1-2). In fact. the Friedel-Crafm a r \ h t i o n offerrocene with oroduct identikcation by thin layer &d open column chromat&aphy is currentlv a o o ~ u l a rundereraduate experiment (3-10). Haworth a i d L ~ Urecently repoFted a high p&formance liquid chromatoera~hic (Ic) s e ~ a r a t i o nof acvlated ferrocenes using .. . "normal-phnw" conditjoni of silica parking and an ethe;: mrthanol mt,hile phase (11-12). T h e incrensiny use of lc in separating components in organic reaction mixtures encouraged us to investigate incorporating this lc separation of ferrocenes into our undergraduate laboratory. However, "normal-phase'' Ic has several disadvantages over t h e more versatile "reverse-nhase" chromatoera~hv. - . . T h e former reauires relatively long column equilibration times and generally necessitates usine non-aaueous mobile ~ h a s e sWe . have developed a reverse-phase separation of these ferrocenes using a C18 bonded t o silica column (pBONDAPAKIC18-Waters Associates) and a far less bothersome mobile phase of methanokwater. A complete introduction t o reverse phase lc may be found in references (13) and (14) Instrumentation A Waters ALCIGPC-204 Liquid Chromatographic with a Model U6K Injector and a Houston Omni-Scribe Model 5211-1 Recorder were used. The prepacked analytical column consisted of Cm bonded to 10 pm silica particles (Waters Associates, Ine., Milford, MA 01757), and the mobile phase was a mixture of methano1:water in a ratio of 3:l. The flow rate was 0.9 mllmin and the absorbance detector was at 254 nm. Experlmental Conditions Since ferrocene acylates readily, the reaction may he investigated at a variety of temperatures from 45Q-100'C. A styrofoam cup serves as an excellent individual constant temoerature bath. The results drsrrilwl her" w r e uhtarned at I(H)Y' with each itudrnt asrignrd a diifcrmt rendon time. Procedure Place 0.2 g (-0.001 mole) of ferrocene, 1.0 ml of acetic anhydride and 0.1 ml of 85%phosphoric acid into a small test tube, cork, shake, and immediately place in a constant temperature bath. At designated onto intervals (15 see. 30 sec. etc.) auench the reaction bv. oaurine . about 5 g crushed ice.~llo& ;he red-brown mixture to stand(with occasional stirring) for 15 min. Filter, wash the solid with 5 ml of cold
of
0 Fe
+ (CHIC)8 I
0
111
SAMPLE:
I. Ferrocene II. Acetylferrocene Ill. l,l'.Diacetylferrocene
Figure 2. Liquid Chromatogram of me Separatim of Standards of Fenacene (I). Acetylferrocene(11). and 1, 1-Diacetylferrocene(Ill).
Table 1. k' and R, Values for Ferrocene and Some Acylated Derivatives Compound Ferrocene (I)
Acetylferrocene (Ii) 1,lDiacstylferrocene(ill)
k'
RI
2.14 1.00 0.64
0.9 0.6 0.3
Table 2. LC Analysis of Products of Acylation of Ferrocene at innOc 7 Product Composition
Readion Time 0.1 min 0.5 min 1.5min 10 min 25 mi"
Fenocene (+)
I+) trace
I-) I-)
AcetyiFerrocene trace (+) (+) (+) (+)
-,
DiacetylFerracene I-) I-) trace I+) (+)
Other (-) (-) (-)
trace I+)
water, and air-dry. Dissolve a small amount of the dry solid in 5 ml of methanol, filter1, and separate by tlc and lc. Results and Discussion Ferrocene acvlates readilv. as is in,. vieldine , " a varietv . of oroduets . dirnrrd in Figure I . A typml rhromnrc,gmm, drpirring rhe separation oi frrroccnr ~ I and I tuu mnjur nrylation prudurrs ~nrrtylfrrn,
