Stability of tobacco casing systems containing palladium

The stability of palladium in tobacco casing systems is improved by the incorporation of a polysaccharide protective colloid.

This invention relates to an improved method for preparing smoking 
compositions comprising tobacco and having associated therewith palladium 
as a catalytic agent. More particularly, the present invention is 
concerned with the use of a protective colloid to improve the stability of 
dispersions of palladium in casing systems used to case, flavor, and 
deposit palladium on the tobacco. 
The subject matter of this invention is related to the subject matter of 
U.S. Pat. No. 4,055,191, granted Oct. 25, 1977; U.S. Application Ser. No. 
763,267, filed Jan. 27, 1977; U.S. Application Ser. No. (Our Ref. : Case 
220-2A) filed on even date herewith, a continuation-in-part of Ser. No. 
(Our Ref. : Case 294) filed on even date herewith. 
As summarized in U.S. Pat. No. 4,055,191, the proportion of polyclic 
aromatic hydrocarbons (PCAH) in the smoke from the combustion of a natural 
leaf tobacco can be materially reduced by incorporating palladium in the 
smoking tobacco composition. It is further disclosed that palladium in 
combination with a nitrate salt, preferably magnesium nitrate, is even 
more efficient in reducing PCAH. Moreover, the smoke condensate collected 
from the smoke of cigarettes composed of tobacco treated with palladium 
and a nitrate salt exhibit a substantially reduced biological activity 
when evaluated on experimental animals according to conventional protocol. 
In the manufacture of cigarettes composed of tobacco treated with palladium 
it has been found that the most efficient and convenient means of applying 
the palladium to the tobacco is to premix the palladium with the casing 
solution and apply this mixture to the tobacco according to conventional 
methods. The practicalities of the commercial production of cigarettes 
from cased tobaccos very often necessitate the storage of the casing 
solution for extended periods at relatively high temperatures before its 
application to the tobacco. In view of the high cost of palladium in 
today's world market the need to maintain the palladium effectively 
dispersed throughout its application and storage periods is of extreme 
importance. 
In the practice of the present invention the stability of "insoluble 
palladium" in conventional casing solutions has been improved by the 
incorporation of a protective colloid of the polysaccharide family in the 
casing system. More particularly, it has been found in accordance with 
this invention that the settling losses of palladium in aqueous casing 
systems is minimized in vessels and pipes during storage and production 
down times by the addition to the casing system of a polysaccharide 
material selected from the groups of natural gums and the alkyl, hydroxy 
alkyl ethers and ester derivatives of cellulose and the alkali metal salts 
thereof.

Accordingly, it is an object of this invention to provide an improved 
method for the manufacture of smoking tobacco compositions containing 
palladium. 
Another object of this invention is to provide a more efficient method for 
depositing palladium on a smoking tobacco. 
A further object of the present invention is to provide a method for 
improving the stability of aqueous dispersions, including but not limited 
to tobacco casing systems, of palladium and its various salts. 
More specifically, an object of this invention is the provision of a method 
for improving the stability of metallic palladium dispersions in 
conventional tobacco casing systems. 
The polysaccharide gums suitable for use in the practice of the present 
invention are the natural, translucent, amorphous bodies exuded by trees 
and other plants. Illustrative of these natural gums are Guar, Agar, 
Algin, Karaya, Guaiac, Ghatti, Tragacanth, and Arabic and mixtures 
thereof. The other suitable polysaccharide materials include the lower 
alkyl and hydroxy lower alkyl ether and ester derivatives of cellulose and 
their alkali metal salts, such as methyl cellulose, hydroxy alkyl 
cellulose and sodium carboxymethyl cellulose. Preferably the 
polysaccharide material is a natural gum, most preferably gum tragacanth. 
The polysaccharide materials contemplated for use in the present invention 
are used in concentrations of from about 0.10 to about 1.0 percent by 
weight, preferably from about 0.2 to about 0.6 percent, of the weight of 
casing applied to the tobacco. This is equivalent to a concentration of 
about 0.005 to about 0.1 percent by weight of the polysaccharide material 
on the cased tobacco. 
Though the subject invention may be used in the manufacture of any tobacco 
composition which has had from 0.001% to about 1% by weight of palladium 
deposited thereon, it has found particular utility when used in the 
preparation of those tobacco compositions and methods described in U.S. 
Pat. No. 4,055,191 to Vello Norman and Herman G. Bryant and U.S. 
Application Ser. No. 13,575, filed on even date herewith by H. G. Bryant, 
P. F. Collins and J. O. Pullman. The complete disclosures of U.S. Pat. No. 
4,055,191 and Application Ser. No. 13,575, are incorporated herein by 
reference. 
The present invention is applicable to any conventional aqueous casing 
system which is used to apply humectants, binders, flavorants and any 
other additives to the tobacco. The casing system with its various 
additives is normally applied to the tobacco in a mixing cylinder at 
elevated temperatures. The mixture of tobacco and casing material is then 
bulked, compressed, cut and then dried to the desired moisture content. 
This final tobacco product at an equilibrated moisture level is what is 
meant by "cased tobacco" as used herein. Preferably the casing system 
should not contain any additive which interferes with the interaction of 
the palladium compound and the reducing agent used to form the "insoluble 
palladium" hereinafter defined. The present invention has found particular 
utility in those instances where the amount of "insoluble palladium" in 
the casing is greater than fifty percent by weight of the total palladium 
in the casing. Though any accurate method for determining the amount of 
palladium may be used the procedure of O. Menis and T. C. Rains, 
"Colorimetric Determination of Palladium With Alpha-Furildioxime," Anal. 
Chem., 27, 1932-34 (1955) has been found to be suitable for determining 
"total" and "insoluble" palladium. 
The palladium may be incorporated into the aqueous casing systems for 
application onto the tobacco in finely divided metallic form, for example 
palladium black, and/or in the form of a salt which is decomposable in 
situ, preferably by heat, into metallic palladium. Water-soluble palladium 
salts are preferred because they are readily soluble in the casing system 
and more evenly incorporated into and distributed throughout the tobacco 
composition. Illustrative examples of suitable palladium salts include 
simple salts such as palladium nitrate, palladium halides such as 
palladium chloride, diammine complexes such as palladous dichlorodiammine 
(Pd(NH.sub.3).sub.2 Cl.sub.2), and palladate salts, especially ammonium 
salts such as ammonium tetrachloropalladate and ammonium 
hexachloropalladate. One form of palladium which has been found to be 
particularly effective in combination with tobacco to provide the smoking 
composition of this invention is ammonium hexachloropalladate, 
(NH.sub.4).sub.2 PdCl.sub.6 (Research Organic-Inorganic Chemicals Corp.), 
99.5% pure. 
The palladium added to the casing system is in amounts sufficient to yield 
on the final cased tobacco a concentration of metallic palladium of 
between 0.001% to about 1%, preferably 0.01% to about 0.1% by weight of 
the cased tobacco. 
Another embodiment of the present invention contemplates the deposition 
onto tobacco of palladium in combination with an inorganic nitric oxide 
generating compound. Illustrative of the nitric oxide compounds which are 
added to the casing system with the palladium in accordance with the 
present invention are the nitrate salts of metals of Groups Ia, Ib, IIa, 
IIb, IIIa, IIIb, IVa, IVb, Va, Vb, and the transition metals of the 
Periodic Table. The particular nitrate salt chosen for use in the practice 
of the present invention is one which is deemed to be non-toxic when 
present in the smoking compositions of the present invention. 
Illustrative of the various nitrate salts which are suitable for use, from 
a toxicity standpoint, in the practice of the present invention are the 
nitrates of lithium, sodium, potassium, rubidium, cesium, magnesium, 
calcium, strontium, yttrium, lanthanum, cerium, neodymium, samarium, 
europium, gadolinium, terbium, dysprosium, erbium, scandium, manganese, 
iron, rhodium, palladium, copper, zinc, aluminium, gallium, tin, bismuth, 
hydrates thereof and mixtures thereof. Preferably, the nitrate salt is an 
alkali or alkaline earth metal nitrate. More preferably, the nitrate is 
selected from the group of calcium, magnesium and zinc with magnesium 
nitrate being the most preferred salt. A magnesium nitrate which has been 
particularly effective in combination with palladium and tobacco to 
provide the smoking composition of this invention is A.C.S. grade 
Mg(NO.sub.3).sub.2.6H.sub.2 O which contains (on a weight basis) less than 
about 0.0005% chloride ion, 0.005% ion and 0.0004% heavy metals 
(calculated as lead). 
The desired concentration of nitrate in the tobacco composition may also be 
achieved by the use of smoking tobaccos which naturally contain relatively 
high concentrations of nitrate in the tobacco. Illustrative of the 
tobaccos possessing a high concentration of native nitrate and which are 
useful in the practice of the present invention are the various burley 
tobaccos, such as those that originate in Germany, Japan and the United 
States; certain Turkish tobaccos, such as those that originate in the USSR 
and Bulgaria; the Maryland tobaccos; and blends thereof with or without 
the various grades of the bright tobaccos. 
Another means of increasing the native nitrate content of the tobacco blend 
involves the use of the processed lower lug portions of the tobacco plant. 
For instance, increasing the content of tobacco burley stems in the final 
blend would result in an increase in the native nitrate content of the 
blend. 
A list of the various tobaccos and their native nitrate content can be 
found in the Tobacco and Tobacco Smoke Studies in Experimental 
Carcinogenesis, by Ernest L. Wynder and Dietrich Hoffman, Academic Press 
1967, the disclosure at pages 453-458 of which is incorporated herein by 
reference. 
In the practice of the present invention, the proportion of nitrate added 
to the casing system or naturally occurring in the tobacco is an amount 
sufficient to yield a concentration below 0.8%, and preferably in the 
range of from about 0.25 weight percent to about 0.75 weight percent, 
calculated as native or added nitrate nitrogen, of the total tobacco or 
tobacco blend. It is preferred to operate in the range of from about 0.50 
to about 0.80 percent total nitrate nitrogen whether in the form of added 
nitrate salt or native to the tobacco. These same concentrations apply 
when the inorganic nitric oxide generating compound is an inorganic 
nitrite salt. 
In addition the present invention contemplates the use of an added 
inorganic nitrate or nitrite salt, or naturally occurring native nitrate, 
or mixtures thereof in combination with palladium in a tobacco 
composition. 
In those instances wherein the entire or predominant portion of the nitrate 
component of the tobacco compositions of the present invention are 
naturally occurring in the tobaccos, i.e. native nitrate, it has been 
found that the addition of a water soluble magnesium salt maybe desirable. 
The magnesium salt can be inorganic or organic provided it is non-toxic. 
Illustrative of these salts are magnesium oxalate, magnesium citrate, 
magnesium chloride, etc. The magnesium is added in amounts sufficient to 
adjust the concentration of magnesium in the final tobacco blend in the 
range of from about 0.5 to about 1.0 weight percent. 
In those instances where the palladium starting material is a water soluble 
palladium salt, it has been found desirable to apply the palladium and its 
carrier medium after the "soluble palladium" in the carrier medium has 
been reduced to not more than 5 percent of the total palladium. The 
carrier medium in most instances will be the casing mixture. The 
insolubilization of the palladium in an aqueous medium is achieved by the 
addition of a reducing agent capable of reducing the soluble palladium 
ions to "insoluble palladium". This insolubilization of the palladium is 
best achieved at temperatures of from about 50.degree. C. to about 
90.degree. C. in a solution having a pH of no more than 3 and by the use 
of a sugar and/or polyhydroxy compound as the reducing agent as described 
in Application Ser. No. (Our Ref.: Case 294), by H. G. Bryant, et.al., 
filed on even date herewith the disclosure of which is incorporated herein 
by reference. 
"Soluble palladium" as used herein can be defined as palladium in an 
aqueous mixture which when the mixture is diluted with water and filtered 
through a membrane filter with 0.45.mu. pores, appears in the filtrate. 
The palladium which is retained on the filter is defined as "insoluble 
palladium". The chemical form of this "insoluble palladium" has been found 
to be predominantly, if not completely, metallic palladium. The chemical 
form of the "soluble palladium" is considered to be essentially all ionic, 
based on available evidence. Though the precise forms of soluble and 
insoluble palladium have not been conclusively established, the present 
invention is intended to extend to "insoluble palladium"formed in the 
manner described, regardless of the precise chemical and physical form of 
the palladium. 
The present invention is of particular utility in those casing systems 
where it is desirable to have high concentrations of insoluble palladium. 
The insolubilization of palladium occurs very slowly at ambient 
temperature, and excessively long periods of time are required to achieve 
practical conversions of the soluble palladium to insoluble palladium. 
Consequently, to achieve practical rates of conversion the solution is 
heated at elevated temperatures, with the rate of formation of insoluble 
palladium increasing with increasing temperature. However, as the 
temperature increases, the insoluble palladium tends to form agglomerates 
of insoluble palladium which presents difficulties in obtaining uniform 
distribution of the metal. The use of the polysaccharide materials 
according to the present invention inhibit the formation of agglomerates 
of palladium thereby providing for a more uniform distribution of the 
palladium in the casing mixture. 
The following examples are set forth to be illustrative of certain 
preferred embodiments and not to limit the scope of the present invention. 
The casing formulas of the examples reported in the following table were 
prepared by premixing the polysaccharide material with the glycerine then 
adding the other casing ingredients with constant stirring. The magnesium 
nitrate should be added prior to the aqueous solution of the palladium 
salt which is the last ingredient to be added to the casing system. The 
casing mixture was stirred and heated at 77.degree. C. for five hours. The 
casing mixture was then removed from the heat source and left undisturbed 
except for periodically withdrawing 0.2 cc samples at depths of 0.5 inches 
below the surface of the casing mixture. These removed samples were then 
analyzed for total palladium. The samples were analyzed for total 
palladium by weighing the removed sample and adding 5 to 10 ml of a 1:1 
volume mixture of nitric and perchloric acids and analyzing for palladium 
by atomic absorption spectroscopy and the results reported in the 
following Table. Any procedure for accurately measuring the quantity of 
palladium in the obtained samples may be used. 
TABLE 
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Example 1 2 Control 
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Casing Formula 
wt. % 
Glycerine 5.03 5.03 5.03 
Invert Sugar 25.53 25.53 25.53 
Corn Syrup 6.91 6.91 6.91 
Flavor 5.32 5.32 5.32 
Gum Tragacanth 
0.20 -- -- 
Sodium Carboxy 
Methyl Cellu- 
lose -- 0.20 -- 
Mg(NO.sub.3).sub.2 . 6H.sub.2 O 
31.86 31.86 31.86 
5% by weight 
solution of 
(NH.sub.4).sub.2 PdCl.sub.4 
.94 .94 .94 
H.sub.2 O 24.21 24.21 24.21 
Stability of 
Pd, wt. % 
in sample 
0 hours 0.424 0.420 0.428 
0.5 hours 0.445 0.408 0.405 
1.0 hours 0.432 0.370 0.382 
17 hours 0.430 0.165 0.042 
72 hours 0.431 0.159 0.039 
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