Arbi Aghazarian
971334160
CHM 331 Lecture Manuscript
Lectures notes from March 28 – 30, 2000
Phospholes are non-planar molecules whereas pyroles are planar. This property can be
explained by looking at the lone pair orbital on phosphorus.
H H H
Pyroles:
N
N
H H H
Phospholes:
planar
H H H
P
P
H H H
nonplanar
H
transition state:
H E
H
planar
Planar derivatives:
Li
Cl2EPh
E-Ph
Li
-PhLi
E
_
CO CO
Li +
BrMn(CO)5
E--Mn--CO
CO
Li
-2CO
CO
hepta 1 complex
/\
E = P,As,Sb,Bi
O
Mn
CO
E
hepta 5 complex
CO CO
The Tolman angle is the angle from a central metal atom (vertical axis) to the farthest
substituent. Thus, larger Tolman angles correspond to bulkier compounds.
Phosphine
Tolman Angle
pKa
US$/g
P(OMe) 3
167
2.60
0.38
PMe3
118
8.65
5.55
PPh3
145
2.73
0.12
(2,4,6-MeC6H2H) 3P
212
7.3
18.36
The pKa can be used to estimate how electron rich phosphorus is. For example, if the
pKa value is low, then equilibrium lies farther to the right: R3PH+  PR3
On the other hand, if the pKa is high, then the equilibrium lies farther to the left.
PMe3 is too strong of an electron donor and therefore, its pKa is relatively high (8.65).
The trimesityl phosphine has sterical bulk, which corresponds to a cone angle less than
180 degrees (the molecule takes up more than 180 degrees of space). Therefore, it forms
a pocket above the phosphorus. Consequently, a proton has difficulty ‘jumping’ onto the
phosphine, and giving the molecule a pKa of 7.3.
Comparison of Wittig Reagents with phosphonium salts
Wittig Reagents:
R3P=CH2  R3P+CH2 Phosphonium salts:
R3P+CH3
The primary difference between these two forms of molecules is that Wittig Reagents are
neutral whereas the phosphonium salts are polar; Wittig reagent have one less H+.
13
C-NMR data for both phosphonium salts and Wittig Reagents indicate that the former
exhibits a frequency of 135Hz and the latter produces a frequency of 153Hz. These
values are proportional to the per cent s character of the C-H bond. It therefore suggests
that Wittig Reagents are not completely ionic but rather covalently doubly bound
(R3P=CH2). /\Hz = 153-135 = +18Hz.
13C-NMR data also reveals that phosphorus ylides are completely different than arsenic
ylides:
Ph3As+CH3
Ph3As=CH2  Ph3As+CH2
142Hz
137Hz
With arsenic, /\Hz = -5Hz which suggests that these ylides are different than those of
phosphorus.
Phosphorus: Coordination # 5
The first phosphorus compounds with coordination number five discovered were
phosphoranes in 1948 by G. Wittig.
PhLi
HCl
HI
Ph3P=O > [Ph4P-O] - Li+ > [Ph4P] + Cl - > [Ph4P]+ I  PhLi
Ph
Ph
Ph
P
Ph
Ph
Wittig, 1948
Things went wrong when Wittig tried to make the methyl compound, but instead, lead to
the historical background of the Wittig Reagent synthesis:
Me
Me
Me
P
Me
-CH4
Me
Me
P
CH2
Me
Me
Today, these reagents are produced by phosphonium salts.
Benzene with one carbon atom replaced with E can give:
E
E
E
E=P, Sb, Bi
Stoudinger Reaction:
R3P: + + - N=N+=N—R’  R3P=NR’ + N2
| H2O (can generate primary amines)
V
Ph3P=O + NH2R’ High yields up to 90%
Michaelis-Arbuzov Reaction
This reaction allows the formation of P—C bonds from compounds that do not
contain P—C bonds
PCl3 + RCl + Na  PR3
PCl3 + RLi RMg*
Hal RHal + P(OMe)3
+ OMe
R P OMe
OMe
Methoxy groups activated
such that they become
electrophiles and halogen
as nucleophile
O
/\
R P
OMe
OMe
Reduction
R P OMe
OMe
Phosphonic acid ester
"Phosphonate"
RHal cannot be PhCl or PhBr but can use PhI with [NiCl3]
Lanthanides
The lanthanides have many applications in industry. For example, the red pigment on a
television screen is a Europium doped compound. Lanthanides are particularly used in
applications because they have f f transitions.
Transition metals have electronic configurations of [Xe]5d16s2 type whereas the
lanthanides have the general configuration of [Xe]f (2+…)6s2.
Ce has the electronic configuration of [Xe] 4f26s2 and Rn: [Xe]4f36s2. Thus, the
lanthanides have the additional f orbitals. They also have +4 oxidation state because it
takes 4 electrons to be removed for Ce to get noble gas Xe configuration.
Lanthanides are non toxic. Their history started in 1794 in Sweden in town of Ytterby
(Ytterby is the town which gave rise to the element Ytterbium hence the name) by mining
engineer J. Gadolin.
Ce has natural abundance of 50ppm in earth’s crust. It is the most abundant Lanthanide
and in comparison to a more familiar element such as chlorine, Ce is half as abundant as
chlorine!
The rarest Lanthanide is Tm: 0.5ppm.%^%&%&^ is the only radioactive lanthanide.
Lanthanides don’t form minerals but can be concentrated from weathering processes,
especially the heavier elements which can form deposits form weathering.
There are two types of deposits: 1. Monazite and 2. Bastnaesite.
The approximate formula for monazite is (La,Ln,Th)PO4 3The formula for bastnaesite is (La,Ln)F-,CO3 2The difference between bastnaesite and monazite is that monazite contains thorium which
is radioactive.
The hazards of monazite: products of decay of thorium; for example, radium .
Other deposits that can be found are SnO2 (Cassiterite) and FeTiO3 (Ilmenite).
Classical Sn producer is Malaysia. One can assume countries that have large Sn reserves
also have Ti reserves. One can also assume countries that have large lanthanide reserves
also have Sn and Ti reserves. The Sierra Nevada Mountains contain the largest and only
mined lanthanide reserve in North America. The largest lanthanide reserve in the world
is located in the People’s Republic of China.
Abundance:
Ce > La > Nd > Pr >……. >Tm
50ppm---------------------0.5ppm
The extraction process of the two deposits are given below:
Monazite:
Monazite
73%NaOH
140 C
Hydrated Oxides
H2O.Ln2O3
added to HCl, until pH=3.5
BaSO4 ppt to remove RaSO4
Impure LnCl3
+
Residue of ThO2
BaCl2 + Ln2(SO4)3
+
Solution of pure LaCl3, LnCl3
Bastnaesite:
Impure Bastnaesite
Dilute HCl to remove CaCO3
Bastnaesite
Heat with
carbon/Cl2
LnCl3
leach with
H2O
Heat in Air
CeO2 + Ln2O3
leach with
0.5M HCl
CeO2
Solution of LnCl3
Solution of LnCl3
It was originally thought that monazite was completely useless except that it was heavy
which was later used as ballasts on ships. However, during world war one, the first use
came in the role of fixed airships where helium was needed but the only sources were the
was oil wells in Luisianna. The need for helium resulted in thefinding that monazite gave
off helium when heated. This phenomena is due to the thorium in the deposit which
produces alpha particles which are nothing but helium particles. Therefore, the monazite
was heated to produce helium and the yields were large: for every gram of monazite, 1L
of He was produced!