Note: Descriptions are shown in the official language in which they were submitted.
=~ ~
-- 1 --
METHOD FOR THE DETECTION AND REMOVAL OF SUF~STITllTION
LABILE TR~NSITION METAL IONS
1. Description:
FIELD OF' INVENTION
- The present invention relates ~o the detection and~or
removal of substitution labile transition metal ions pr~sent
in aqueous solutions. More specifically, the metho~
described herein concerns the use of a 2-pyridinethiol-1-
oxide anion to determine the presence of said transition
metal ions and to facilitate their removal from solution
by chelation. Most specifically, the present invention
relates to the detection/removal of said transition metal
ions from an aqueous solution also containing other che-
lating agen~s, or from aqueous solutions into which other
chelating agents will be added, the use of a 2-pyri~inethiol-
l-oxide alkali salt being compatible with said other chelating
agents.
BACKGROUND OF THE INVENTION
Industrial, household and cosmetic preparations are
often sensitive to the presence of heavy metal ions; which
iOllS interfere with active agents resulting in a ~imun.iti.on
or loss of product effectiv~ness. The nature of the inter
ference caused by the metal ions is varied, for example,
the breakin~ of emulsions in furniture polishes, hand cr2ams
or lotions, Friede~-Crafts reactions that affect fragranc~
stability, or xeduction in peroxide stability.
Metal ions which behave in this manner are the substi-
tution labile transition metal cations, for example, some
complexes of ferric and ferrous, and cupric ions. Substitu-
.......
~4
-- 2
tion inert cations, for example, the chromic ion, ~o not
complex or transchelate with organic ligands, ancl therefo~e
do not require removal from the aqueous solution. Whether
an ion is substitution labile or substitution inert depends
on the d orbital con~igura~ionl subs-titution inert ions
being characterized by 3 and 8 d electrons in their outer
shell. Transition metal ions having 4, 5 an~ 6 d electrons
in the outer shell ~re also substitu~ion inert if complexed
with strong field ligands such that the electrons in those
d orbits are paired.
Substitution labile ion contamination in the prepara-
tion of these products typically occurs during man~lfacture,
the ions being present in the process water arriving from
outside the facility battery limits. The contamination may
also occur because of the nature of piping and equipment
materials used witin the battery limits of the processiny
~aeility. Of course, if the magnitude o~ in-plant contamin-
ation is too great, replacement of equipment may be more
economical than removal of the ions by chemical/physical
means. ~roduct contamination may occur during storage or
shipment from the product containers, especially metal
containers having a polymeric film that ean be seratched.
Past practice has sought to eontrol the dimunition/
loss in produet effectiveness caused by ion contamination
by several means. Process water entering the facility can
be treated by distillation or ion exchange, thereby removing
the contaminants. A second method, often used in conjunction
with water treatment, has been to incorporate within -the
product composition a chelating agent that complexes the S
substitution labile transition metal ion thereby reducing
offending physical or chemical interference. Typical
chelating agents are alkali salts of nitrilotriacetic acid,
,
: ~ ~ !
. . ,
~2~
-- 3 --
ethylenediaminetriace-tic acid and the like. In cer~ain
formulations the incorporation of these chelating agen~s
are also necessary even though -the processing water and
facility have been successEully purged of the substitution
labile ions. Instances where the chelating agent would be
required are where the product is shipped in containers which
may allow the ions to enter into the product solution,
where the product is used in an aqueous environment that may
contain the metal ions, or where the chelating a~ent --
itself is an active ingredient of the formulation.
Greater flexibility in the manufacture of the afore-
said chemical preparations could be achieved if ~here
was a simple method whereby the substitution labile ions
could be identified prior to the use of the process water
in the product batch. SimiIarly, the manufacture of these
formulations would be simplified if the ions could be
removed without resorting to expensive distillation and/or
ion exchange methods. Because the formulations themselves
may con-tain a chelating agent, it is critical that -the
method used to detect or remove the substitution labile
metal ions does not itself deactivate other ~helating
agents present in solution or that are to be aclded to the
final product formulation. The detection,/removal means
should also be inert to the other active and non-active
constituents;of the formulation, should be usable over a
wide pH range, and should not exhibit off odors.
SU~ARY OF INVENTION
It is an object of this invention to provide a method
for the detection and/or removal of substitution labile
heavy metal transition ions from an aqueous solu-tionO
It is a urther object of this invention to provide a
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method for the detection or ~emoval of the aforesaid ions
from an aqueous solution, which method is compatible with
the presence of other chelating and sequestering agen~s.
The primary objec~ of the in~en~ion is to detect or
remove the aforesaid me~al ions from an aqueous solution
by the addition ofan effective amount of an ionizable salt
of a 2-pyridinethiol-1-oxide compound, specifically an
alkali salt of 2-pyridimethiol~l-oxide, the presencP of which
does not interfere with the use of or incorpora$ion of other
10 chelating or sequestering agents.
These and other objects and advantages of the present
invention will be readily apparent upon a reading of the
detailed description of invention, a summary of which
~ollows~ .
The method of detecting the presence of a subs titution
labile metal ion comprises the step of adding an effective
amount of an ionizable salt of 2-pyridinethiol-1-oxide, the
presence of said salt being compatible with the presence
or subsequent addition of !helating or sequestering agents
20 having a higher equilibrium constant for the ion to be
complexed than said salt anion. The presence of said
ion is confirmed by the formation of a precipitate which
typically is highly coloredu Removal of the complexed
ion from $he a~ueous solution may then be accomplished
by distillation, filtration, centrifuging, or ~ther means
used to separate a solid ~rom an aqueous phaseO
- 4a -
In one aspect the invention provides a method of deter-
mining the prese~ce or absence of substitution labile transition
metal ions in process water to be u~ed in the manufacture
of chelating or sequestertng agent containing preparations,
the method comprising the steps of (a~ con~acting said process
water with an e~fective amount of an i onizable salt of
2-pyridinethiol-1-oxide, said chelating or sequestering agent
in the preparations being selected from the group consisting
of phosphate salts, citrate salts, nitrilotriacetic acid and
salts thereof, and ethylenediaminetetraacetic acid and salts
thereof, the presence of the anion of the ionizable salt of 2-
pyridinethiol-l-oxide being compatible with said chelating or
sequestering agent, which agent has a higher equilibrium constant
: for said subs-titution labile transition metal ions than fox the
salt anion, and (b) observiny whether a precipitate is formed by
reaction of said metal ions and said salt anion, whereby the
.,
presence of said substitution lab~le transit~on metal ion is
confirmed by the formation o~ a precipitateO
.~ In another aspect the invention provides a method of
determining the suitability of process water to be used in
the manufacture of industrial, household, or cosmetic pre-
parations that contain a chelating or seques~ering agent, the
method comprising the steps of (a) contacting said process water
to be used in the manufacture of said chelating or sequestering
agent containing industrial, household, or cosmetic preparations
with an effective amount of an ionizable salt of 2-pyridinethiol-
l-oxide, said process water being unsuitable in the presence of
substitution labile transition metal ions selected from the
group consisting o~ Fe , Fe , Mn , Cr ~ or mi~tures thexeof,
said chelating or sequestering a~ent in the preparations being
selected from the group consisting o~ phosphate salts, citrate
- ~b
salts, nitrilotriacetic acid and salts thereof~ and
ethylenediaminetetraacetic acid and salts thereof, the presence
of the anion of the ionizable salt of 2~pyridinethiol-oxide
being compatible with said chelat;ng or sequester.ing agent,
which agent has a higher equilibrium constant for said sub~
stitution labile metal ions t~an ~or the salt anion; (b)
observing whether a precipitate is formed by reaction of said
substitution labile transition metal ions and said salt anion;
and (c) rejecting said process water for use in the manufacture
of said preparations i~ a precipitate is formed.
~ETAILED DESCRIPTIiON OF INVENTION
.
In accordance with this in~ention, it has been found
that ionizable salts o~ 2-pyridinethiol-1-oxide (herein
after pyridinethiol) when added to an aqueous solution
containing substitution labile transition metal ions,
1 C +2 Ti~3 V~3 Mo~5~O+6~CU ions, forms
a highly colored precipi~ate ~hereby indicating the presence
of said ions. It has also been found, that the prese,lce
of the pyridinethiol in the agueous solution is compatible
with many chelating and sequestering agents used currently
in the production of household, industrial, and cosmetic
preparations, which compatibility is not predicted by
chemical or thermodynamic rate laws.
The preferxed form of pyridinethlol used in the detection
of the substltut.ion labile ions has the structural f~rmula
in tautomeric form as follows:
[~5
b o
where X is an alkali Group I metal of sodi~m, postassium,
and lithium. Pyridinethiol compounds are gol~ under the
Omad.ine trademark, e.g., Sodium Omadine~l/ by Olin Chemicals,
Stamford, Connecticut. As disclosed in ~'R~te and Mechan~
isms of Substitution of Inorganic Complexes in Solukion",
Ho Taube Chemical Reviews, pages 69-126 (1952), the
kinetic~ governing rates of chelation are determined
primarily by d orbital configurationO Metal complexes
requiring positive crystal field stabilization enerqy in
their activated complex exchange inner sphere ligands
very slowlyO Such complexes are substitution inert.
Metal complexes possessing 3 and 8 d electrons in thei.r
outer shell are substitution inert a Finally~ transition
metal ions poss2ssing 4, 5 and 6 d electrons in their outer
shell that are complexed with strong field liyands, or
example, metal complexes wherein 4~ 5 and ~ d electrons
are paired, are also substltution inert~ Substitution
i t ~ ~ v-~2 C ~3 Mo+3 W~3 Re+4;~n~4 a~e ~o~
} r~
~2~
subject to transchelation, and do not interEere in the
chemical preparation under consideration. Metal transition
ions not within the above definition of substitution inert
ions are considered to be substitution labile, and will
adversely affect the effectiveness of the household,
industrial or cosmetic preparation. Depending upon the
active ingredients in said preparations, the substitution
labile ions can cause emulsified preparations to split into
two phases, may combine chemically with expensive dyes,
perfumes, or aromatic materials or may reduce the stability
of other active ingredients. For this reason, many pre-
parations include in their formulation a chelatinq agent
or sequestering agent that sacrificially complex with these
ions to decrease their interference. Even though the
chelating or sequestering agents are added to the prepara-
tion formula, flexibility in manufacture of these composi-
tions would be enhanced iE the manufacturer could determine
a priori whether the process water contains the substitu-
tion labile ions. For example, if the process water does
not contain these ions, the addition of the chela-ting agent
may be dispensed with or a lesser amount of the chelating
ayent could be used. Alternatively, if substantial amounts
of the ions are present in the process water, the manufacturer
could attempt to remove the ions by ion exchange or by
the method of the present invention. However, -the method of
the present invention for detecting the presence of the ions
does place into solution and into the preparation an effec-
tive amount of the pyridinethiol, a relatively weak chela-
ting agent, and subsequen-t addition of other chelating or
sequestering agents should not result in transchelation
of these materials especially where the chelating or seques-
tering agent is an active ingredient of the -formulation.
The rate of chemical conversion of reactants to products
is determined empirically, and is described by chemical
- 7
kinetics. Observed reaction rates are quantified as rate
laws. Conversely, thermodynamic equilibrium measures the
po~ential or driving force of a chemical reaction; i.e.
it predicts the tendency to form one reaction product
over another~ The potential ox driving force of the chemical
reaction is measured by equilibrium constants~ the larger
the equilibrium constant, ~he greater the driving ~orce to
obtaill equilibrium. The table below provides equilibrium
constan~s for several transi~ion metal chelating agents
10 common7y used ana various metal ions, as well as the equil-
librium constants fnr pyridinethiol.
Equilibrium Constants
for
M~t~- Co~
Chelating Liyands H Co~2 Fe~2 zn~2
2-Pyridinethiol-l-Oxide 4.5 10.0 4.7 11.3
Thioglycolic Acid 13.2 12.4 10.9 1599
Dithizone 15.0 13.0 - -
Sodium Nitrolotriacetate(NTA) 13.0 14.2 8.8* 10.4*
20 Sodium Ethylenediamine
tetracetate (EDTA) 10.2 16.2 14~3 16~4
Ethylene Diamine17.5 1400 9.6 11.5
1, 10-phenanthroline 4~9 l9o9 21~0 18.5
*Value for Kl
Inspection of this Table indicates that the pyridinethiol
anion is a relatively weak ligand, and thermodynamically, a
metal complex of the pyridinethiol should react with ano~hex
chelating agent havi.ng a higher equilibrium constant to form
the metal complex of that chelating agent. Hence, an
analysis of the thermodynamic data would predict that when
pyridinethiol is in solution with another chelating agent
specified in the table, complex forma-tion would always
favor ~he chelating agent at the expense of pyridinethiol.
That is the use of the pyridinethiol to provide an indication
of the presence of metal complexes would subsequf~ntly, after
the addition of one of the above chelating agents, reduce
or eliminate the effects of pyridinethiol. Based upon
thexmodynamic considerations, the following chemical reac-
tions should take place with octahedral metal complexes:
[M P3] ~nC _ ~ MCX+3P (13 Transchelation of
pyridinekhiol
Mx ~ 3p ~C - McX ~ 3p- t2)-Competing equilibrium
n favoring the thermo-
dynamic~lly more stable
chelatlng agent
while the reaction below should not be ~avored:
MCn ~ 3P ~ ~~ [MP ]X-3~ C 13) Transchelation to
form the pyridine-
thiol complex
where ~5 is the substitution labile ion, C is a chelating
agent, and P is a pyridinethiol anion, and where x is the
charge of -the substitution labile ion and n is ~h~
coordinating power of the chelating agent.
Equa~i~n 1 indicates t.hat pyridinethi.ol complexe~ with a
substitution labile transition metal ion and in a solution
with a chelating agent (C~ having a higher equilibrium
constant than the metal-pyridinethiol complex should trans-
chelate to form a metal complex of said chelating agent~
Equation 2 indicates that a solutiol of metal ions, pyridi-
nethiol, and a chelaking agent should preferenkially form
the chelating agent-mekal complex. Equation 3 indicates
- 9 -
that a c~lelating agen~-metal complex in sol.ution should
not transchelate with pyridinethiol to form the pyridi-
nethiol complex.
i
These arguments are based upon equilibriurn constant
data and provide a good basis for predicting the outcome
of a chemical reaction. Thermodynamics can pred.ict the
stability of a complex but cannot assure that a given
reaction will in fact occur. As p.reviously stated,
chemical kenitics emperically measures a reaction and
quantifies it as a rate law whereas thermodynamics can only
predict how fast equilibrium is obtained. if the reac~ion
takes place. Analysis of the above principals with respect
to stability and transchelation has not been considered
heretofore, apparently because there has been no particular
interest in the rate and equilibrium aspects of pyridinethiol
chemistry vis-a-vis other chelating agents. From the
examples hereinafter described, it was found that the pyri-
dinethiol anion behaves in an unusual and unexpected way.
In the competing reaction of Equation 2, it was found that
the substitutlon labile ion did not complex with the
chelating agent, but rather formed an insoluble precip.itate 1i
with the pyridinethiol: ,
M -~ nC -~ 3P -~ [MP3] ~-~ Cn (4)
while the transchel.ation reaction of Equation 3 did in
fact take place forming the pyridinethiol metal complex:
MCn + 3P ~ [MP3] l~ nC ~5)
Again, the complex formed was insoluble. Thus, it can be
seen that pyridinethiol/ which forrned a highly col~r~d pre-
cipitate of the substitution labile metal ion, could be
used to indicate the presence of the ion, ye-t would not
~2~
~ 10 -
c;ubs~ ent-ly react- ~r krarll;ch~lat:n wit}l .~e~ etll-erir)~3 aclentr~
or chelating agents place~ in-to soIution.
. .
Detection of substitution labile transition metal
ions can be accomplished by adding to the aqueous solution
an effective amount o the pyridinethiol anion,
followed by visual or instrumen-t observation of the forma-
tion of the precipi~ate, ~ypically also associated with a
color change. Precipitates possess a range of colors:
green (cupric); blue (ferrous); blue-grey (ferric). To
remove the ions from solution, the pyridinethiol can be
added to the process water to form the precitptate, followed
by removal of the precipitate by conventional means, for
example, by distillation, filtration or centrifuging. The
amount of pyridinethiol anion added to the pro~ess water
is dependent upon whether detection or removal is desired.
Where detection is the primary purpose of the acldition, the
pyridinethiol can be added in small concentrations, it only
being necessary to obtain the color change and the formation
of the precipitate. ~ere removal of the substitution labile
ions is desired, the pyridinethiol should be added in excess
to ensure complete precipitation of all substitution labile
ions in solution. `'
The following examples illustrate reactions t4) and
(S) described above.
~XAMPLE_I
Two solutions were prepared; solution A and solution
B described below:
Solution A
Item Parts by Weight
Deioni2ed Water 85.20
Sodium 2-Pyridinethiol-l-Oxide (40%) 0.03
Disodium Ethylenediaminetetra- -
acetate Hydrate (EDTA salt) 0.04
85027
Solution B
Item Parts by Weight
Deionized water 14.705
Fe2~504)3 9~120 0.025
14.730
Solution B was added to a buret and titrated in-to Solution A.
Immediately after addition, a blue color appeared due to the
formation of the ferric 2-pyridinethiol-l-oxide complex.
The order of addition was then reversed and the chelating agents
were added to a solu-tion of ferric sulfa-te. As before, -the
results were the same. Shortly after addition, the formation
of an insoluble dark precipitate was noted. It was con-
cluded that -the ferric ion did not preferentially complex with
EDTA, even though equilibrium constant data would suggest
thermodynamic driving force according to Equation 2 was in
favor ofthe EDTA com,le~.
-
EXAMPLE II
This example was conducted to test transchelation of
a substitution labile metal ionO Two solutions were pre-
pared; solutions C and D described below:
Solution C
Item Parts by Weight
Deionized water 89.905
Disodium EDTA .2H2O 0.040
Fe2~S4)3 91~2 _0 025
89.970
Solution D
Item Parts by Weight
Deionized water 10.000
Sodium 2-Pyridinethiol-l-Oxide (40%) 0.030
10.030
Ferric EDTA was formed and solution D containing the pyrid-
inethiol anion titrated into solution C. Immediately after
addition, a violet color was observed and a precipitate
formed. As before, the order of addition was reversed, and
with the same results. The conclusion is that the substitu-
tion labile ferric EDTA complex transchelated to form the
insoluble ferric 2-pyridinethiol-1-oxide complex which
subsequently precipitated from solution according to reac-~ion
(5).
- 13 -
F,X~M~
To test the subs~itution inertness of the ferrous and
ferric ion when complexed with s-txong field ligands, the
following experiment was conducted:
Solution E
Item Parts by Weight
Deio~ized ~ater 89.94
K3Fe(CN)6 0.03
89~97
Solution F
Ite_ Par-ts b~ Weight
Deioni7ed water 89.93
K4Fe(CN)6 3H2 0 04
89.97
Solution G
Item Par-ts by Weight
Deionized water 10.000
Sodium ~-Pyridinethiol-l-Oxide (40%) 0.030
10.030
Solution G was added to solution E and solution F.
Unlike the results obtained with Examples I and II, after
40 minutes no color change or precipitate was observed.
.
.. .... .. ...
r~
This led -to the conclusion tha~ cyanide is a strong field
ligand and will make the ferrous/ferric complexes substi-
tution inert, i~e. cyanide causes the 5d and 6d electrons
to be paired. When these compounds were added -to a solution
of pyridinethiol anion, no reaction oc~urred because com-
plex formation and subsequent precipitation can only occur
with substitution labile transition metal ions. This was
confirmed by preparing a solution of chromic chloride,
which was added to a disodium EDTA solution. When solution
G was added to this mix-ture, no color change or precipitate
was observed after 30 minutes. This was because the chromic
ion, d , is substitution inert and like ferric cyanide and
ferrous cyanide will not transchelate with pyridinethiol.
EXAMPLE IV
The industrial applicatlon of the invention was tes~ed
by the following experiment in which solutions H, I, J and
K were prepared.
Solution H
Item Parts by Weight
Deionized water 70.00
~nion Carbide Silicone Emulsion
LE-45~ (~0%) 5.00
Fragran~e 0.20
Sodium 2 Pyridinethiol l-Oxide (40%) 0.03
75.23
Soluti.on I
Item Parts by Weight
Deionized water 14.710
CUS4 5H2 0.020
1~.730
Solution J
Item Parts by Weight
Deionized water 14.685
Sn Cl2.2H~O 0.020
FeSO4.7H2O 0.025
14.730
Solution K
.
Item Parts b~ Weight
Deionized water 14.70S
Fe2(So4)3 9H2 0.025
14.730
When solùtion I, J, or K containing substitution labile
ferric, ferrous, or cupric ions was added to solution H
containing the pyridinethiol, an immediate color change was
noted and a precipitate formed. The odor of the resultin~
mixture was noted after 30 minutes and after 18 hours, and
such organoleptic condition was comparable to the control.
The colored precipi~ate ranged from green tcupric) to blue
(ferrous) to grey ~ferric)~ Solu-tion H is typical of a
light duty polishing cl.eaner containing a silicone emulsion.
r~
- 16 ~
Typically transition metal ions would destabiliz~ the silicone
emulsion so that the water used in the formula-tion must be
controlled.
The above description of Lhe invention is exemplary
only, the scope of the invention not being limited except as
described in the claims that follow.
