Dissociation of naphthoic acids in non-aqueous media. Comparison of benzene and naphthalene skeletons

Article abstract of DOI:10.1135/cccc20000385

Seven monosubstituted 1-naphthoic acids were synthesized by new or modified procedures, and their dissociation constants were measured potentiometrically at 25 °C in methanol, acetonitrile, dimethylformamide, and pyridine. Dissociation constants of these along with thirteen substituted 1-naphthoic acids and twenty-five substituted 2-naphthoic acids previously studied were measured at 25 °C in ethanol and dimethyl sulfoxide. The pK_HA values of 3-and 4-substituted 1-naphthoic acids were treated by simple linear regression and principal component analysis, and the results were used for comparison of model compounds and of corresponding 3-and 4-substituted benzoic acids with the aim of comparison of benzene and naphthalene skeletons. It has been found, the 3 and 4 positions of the 1-naphthyl system can roughly be compared with the meta and para positions of benzene, respectively.

Full text of DOI:10.1135/cccc20000385

Dissociation of Naphthoic Acids
385
DISSOCIATION OF NAPHTHOIC ACIDS IN NON-AQUEOUS MEDIA.
COMPARISON OF BENZENE AND NAPHTHALENE SKELETONS
b
a2
Patrik PAŘÍKa1,* Jitka WOLFOVÁ and Miroslav LUDWIG
a
Department of Organic Chemistry, University of Pardubice, nám. Čs. legií565,
1
2
532 10 Pardubice, Czech Republic; e-mail: patrik.parik@upce.cz, miroslav.ludwig@upce.cz
Department of Organic Chemistry, Masaryk University, Kotlářská 2, 611 37 Brno,
Czech Republic; e-mail: wolf@chemi.muni.cz
b
Received Jan uary 17, 2000
Accepted March 10, 2000
Seven m on osubstituted 1-n aph th oic acids were syn th esized by n ew or m odified procedures,
an d th eir dissociation con stan ts were m easured poten tiom etrically at 25 °C in m eth an ol,
aceton itrile, dim eth ylform am ide, an d pyridin e. Dissociation con stan ts of th ese alon g with
th irteen substituted 1-n aph th oic acids an d twen ty-five substituted 2-n aph th oic acids previ-
ously studied were m easured at 25 °C in eth an ol an d dim eth yl sulfoxide. Th e pKHA values of
3- an d 4-substituted 1-n aph th oic acids were treated by sim ple lin ear regression an d prin cipal
com pon en t an alysis, an d th e results were used for com parison of m odel com poun ds an d of
correspon din g 3- an d 4-substituted ben zoic acids with th e aim of com parison of ben zen e
an d n aph th alen e skeleton s. It h as been foun d, th e 3 an d 4 position s of th e 1-n aph th yl sys-
tem can rough ly be com pared with th e meta an d para position s of ben zen e, respectively.
Key w ord s: Naph th oic acids; Ben zoic acids; Dissociation ; Ion ization con stan ts; Substituen t
effects; Solven t effects; Ch em om etrics.
Th e h istory of description of substituen t effects in n aph th alen e derivatives
starts from th e Ham m ett equation . At first, th e properties of n aph th alen e
derivatives were related to th e correspon din g ben zen e derivatives with th e
presum ption th at th e way of tran sm ission of substituen t effects is iden tical
or very sim ilar in both system s1. Later on , th e reaction con stan ts ρ describ-
in g th e ben zen e series were used to calculate various position -depen den t
con stan ts σ, σij, σn or σN for th e n aph th alen e skeleton 2–9. Th e presum ption s
from wh ich th e defin ition of th e said con stan ts started, i.e., th e equality of
reaction con stan ts ρ for ben zen e an d n aph th alen e derivatives7,10, h owever,
proved to be n ot quite justified. In spite of th at, th e reactivity of n aph th a-
len e derivatives con tin ued to be com pared with th at of th eir ben zen e an a-
logues, wh ich is docum en ted by several selected papers from th e area of
study of carboxylic acids1,4,5,7,10–13. Such a com parison can also be based on
studies of acid-base properties of n aph th oic an d ben zoic acids in n on -
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

386
Pařík, Wolfová, Ludwig:
aqueous m edia. Our previous paper14 gave dissociation con stan ts of 38 sub-
stituted n aph th oic acids in four organ ic solven ts, an d th e data obtain ed
were used to exam in e th e substituen t effects on dissociation of m odel com -
poun ds in n on -aqueous m edia usin g th e Ham m ett equation .
Th e presen t paper tries to exten d th e scope of both th e series of com -
poun ds in vestigated an d th e n um ber of n on -aqueous m edia used in dissoci-
ation of n aph th oic acids, an d deals with a com parison of acid-base
properties of 3- an d 4-substituted 1-n aph th oic acids an d 3- an d 4-substitu-
ted ben zoic acids with th e em ph asis on fin din g th e differen ces between ef-
fects of th e n aph th alen e an d ben zen e skeleton s.
EXPERIMENTAL
Th e m odel com poun ds, except for th ose given below, were prepared by usual procedures.
Th eir structure was verified by 1H an d 13C NMR spectra m easured with a Bruker AMX 360
apparatus. Th e dissociation con stan ts (pKHA) of twen ty 3-, 4-, 5-, an d 8-substituted
1-n aph th oic acids an d twen ty-five 4-, 5-, 6-, 7-, an d 8-substituted 2-n aph th oic acids were de-
term in ed at 25 °C by th e m eth od of poten tiom etric titration usin g an autom atic apparatus
TITRALAB 3 (Radiom eter), th e experim en tal arran gem en t an d electrodes used bein g th e
sam e as th ose in our previous papers14–17. Th e solven ts used were purified in stan dard ways.
3-Am in o-1-n aph th oic Acid
3-Am in o-1-n aph th oic acid was prepared accordin g to ref.18 except for th e step leadin g to
3-n itron aph th alen e-1-carbon itrile. Th us, n aph th alen -1-am in e (61.3 g, 0.428 m ol) was acety-
lated an d brom in ated to give 4-brom on aph th alen e-1-acetam ide (101.7 g, 0.385 m ol), wh ich
was tran sform ed in to 4-cyan on aph th alen e-1-acetam ide (60 g, 0.285 m ol). Th e latter com -
poun d was n itrated an d h ydrolyzed to give 4-am in o-3-n itron aph th alen e-1-carbon itrile
(27.3 g, 0.128 m ol), wh ich was th en diazotized. Th e diazon ium salt was added durin g 30
m in at –5 °C in to a suspen sion of h ypoph osph orous acid prepared by addin g dropwise a so-
lution of NaH2PO2·H2O (66.7 g) in water (150 m l) in to a m ixture of con cen trated sulfuric
acid (41 m l) an d water (41 m l) at –5 °C. Th e reaction m ixture was left to stan d 3 days in
cold place. Th en th e separated solid was collected by filtration , wash ed, dried, an d
recrystallized from eth an ol with ch arcoal. 3-Nitron aph th alen e-1-carbon itrile was prepared in
30% yield (7.5 g), m .p. 184–189 °C (ref.18 m .p. 183 °C). Th e n itrile was h ydrolyzed to
3-n itro-1-n aph th oic acid (5 g, 0.023 m ol), wh ich was th en h ydrogen ated in m eth an ol with
palladium as a catalyst to give 3-am in o-1-n aph th oic acid (3.2 g, 0.017 m ol).
3-Ch loro-1-n aph th oic Acid
First, 3-n itron aph th alen e-1-carbon itrile was reduced to 3-am in on aph th alen e-1-carbon itrile
accordin g to ref.19. Th is am in on itrile was also prepared, in a com parable yield, by th e fol-
lowin g procedure. A m ixture of FeSO4·7H2O (35.5 g) an d water (43 m l) was h eated to boil-
in g with in ten sive stirrin g an d treated with
a suspen sion of 3-n itron aph th alen e-
1-carbon itrile (3 g, 0.015 m ol) in con cen trated aqueous am m on ia (20 m l) added dropwise
with in 10 m in . Th en con cen trated aqueous am m on ia was added un til th e m ixture was alka-
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

Dissociation of Naphthoic Acids
387
lin e (pH 12), an d th e boilin g was con tin ued for an oth er 15 m in . After coolin g, th e m ixture
was filtered, th e filter cake was dried an d extracted with dieth yl eth er. After distillin g off th e
eth er, th e crude product was recrystallized from eth an ol with ch arcoal. In th is way, we pre-
pared 0.8 g of 3-am in on aph th alen e-1-carbon itrile (31%) with m .p. 118–122 °C (ref.8 m .p.
116–117 °C). Th e product was tran sform ed in to 3-ch loron aph th alen e-1-carbon itrile an d
th en to 3-ch loro-1-n aph th oic acid20
.
4-Nitro-1-n aph th oic Acid
4-Nitron aph th alen -1-am in e was tran sform ed in to 4-n itron aph th alen e-1-carbon itrile by th e
San dm eyer reaction 21. Th en , 4-n itron aph th alen e-1-carbon itrile (2 g, 0.010 m ol) was h eated
with con cen trated sulfuric acid (10 m l), glacial acetic acid (10 m l), an d water (10 m l) at
120 °C for a period of 4 h , wh ereupon th e reaction m ixture was poured on to crush ed ice (ca
50 g), an d th e separated solid was collected by filtration an d dissolved in 5% aqueous so-
dium carbon ate solution (70 m l). After clarification , th e solution was acidified with h ydro-
ch loric acid to pH 1, th e separated solid was collected by filtration , an d recrystallized from
m eth an ol with ch arcoal. Th e 4-n itro-1-n aph th oic acid th us prepared (0.8 g, 37%) h ad m .p.
225–227 °C (ref.10 m .p. 221–223 °C).
4-Meth yl-1-n aph th oic Acid
A m ixture of n aph th alen e-1-carbaldeh yde (47.5 m l, 0.350 m ol), eth an e-1,2-diol (350 m l),
80% h ydrazin e h ydrate (35 m l), an d NaOH (46.7 g) was h eated on a boilin g water bath for
30 m in an d th en refluxed for 3 h . After coolin g, th e m ixture was treated with water (300 m l)
an d extracted twice with dieth yl eth er (200 m l). After distillin g off th e eth er, th e crude
p rod u ct was d istilled in vacu u m to give 26.7 g (54%) of 1-m eth yln ap h th alen e, b.p .
106–109 °C/1.5 kPa (ref.22 b.p. 111 °C/1.6 kPa). 1-Meth yln aph th alen e was th en acetylated
to give 1-acetyl-4-m eth yln aph th alen e23
.
A m ixture of NaOH (4.8 g), water (60 m l), an d crush ed ice (60 g) was treated with bro-
m in e (2.4 m l). After th e brom in e was dissolved, th e m ixture was treated with 1-acetyl-
4-m eth yln aph th alen e (3.3 g, 0.018 m ol) added at 50 °C, an d th e reaction m ixture was
refluxed for 1 h . After coolin g, th e solution was wash ed with dieth yl eth er (100 m l) an d
acidified with h ydroch loric acid to pH 1. Th e un reacted h ypobrom ite was rem oved by addi-
tion of Na2S2O5. Th e separated solid was reprecipitated from a 5% aqueous sodium carbon -
ate solution by addition of h ydroch loric acid, an d recrystallized from 70% aqueous eth an ol
with ch arcoal to give 0.7 g (21%) of 4-m eth yl-1-n aph th oic acid, m .p. 168–176 °C (ref.24 m .p.
176–177 °C).
5-Meth oxy-1-n aph th oic Acid
1-Nitron aph th alen e was brom in ated25 to give 1-brom o-5-n itron aph th alen e, wh ich was th en
reduced to 5-brom on aph th alen -1-am in e26. A m ixture of th e latter (15 g, 0.068 m ol), CuCN
(6.4 g), an d pyridin e (5.8 m l) was h eated at 190 °C for 1.5 h . Th e h ot reaction m ixture was
tran sferred in to dilute aqueous am m on ia (200 m l), th e solid was crush ed an d th e suspen sion
was left to stan d overn igh t. Th en th e solid was collected by filtration , wash ed with dilute
aqueous am m on ia an d water, an d recrystallized from 50% aqueous eth an ol. Th e yield was
5.7 g (50%) of 5-am in on aph th alen e-1-carbon itrile, m .p. 129–135 °C (ref.27 m .p. 141.5–145 °C).
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

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Pařík, Wolfová, Ludwig:
A com parable yield of 5-am in on aph th alen e-1-carbon itrile was also obtain ed by th e proce-
dure accordin g to ref.27
.
5-Am in on aph th alen e-1-carbon itrile was tran sform ed in to 5-h ydroxyn aph th alen e-1-carbo-
n itrile, wh ich was th en h ydrolyzed to 5-h ydroxy-1-n aph th oic acid, an d subsequen tly m eth -
ylated to 5-m eth oxy-1-n aph th oic acid28
.
RESULTS AND DISCUSSION
Tables I an d II sum m arize th e dissociation con stan ts of m on osubstituted 1-
an d 2-n aph th oic acids in th e form of pKHA (alon g with th e stan dard devia-
tion s) foun d in th e in dividual solven ts. Th e series of so far publish ed
n on -aqueous m edia selected for th is study – m eth an ol (MeOH), aceton itrile
(AN), N,N-dim eth ylform am ide (DMF), an d pyridin e (Py) – was exten ded by
am ph iprotic eth an ol (EtOH) an d dipolar aprotic protoph ilic dim eth yl
sulfoxide (DMSO).
Th e pKHA values obtain ed (each m easurem en t was repeated th ree tim es)
were treated by lin ear regression . Th e dissociation con stan ts were correlated
usin g th e Ham m ett equation with th e substituen t con stan ts σm,p (ref.29)
foun d for th e ben zen e derivatives. Th e average dissociation con stan ts pKHA
were an alyzed by th e m eth od of projection to laten t structures30 (PLS).
A m ere com parison of acidity of both n aph th oic acids an d ben zoic acid
in th e m edia studied clearly sh ows an acidifyin g effect of th e n aph th alen e
skeleton as com pared with th at of th e ben zen e rin g. Th e respective values
of dissociation con stan t (pKHA) of 1-n aph th oic acid, 2-n aph th oic acid, an d
ben zoic acid are: in MeOH 8.92, 9.39, an d 9.41; in DMF 12.00, 12.11, an d
12.27; in Py 9.49, 9.74, an d 9.81; in AN 20.13, 20.30, an d 20.70; in EtOH
9.87, 10.15, an d 10.25; in DMSO 10.63, 10.85, an d 11.00 (th e values for
ben zoic acid were taken from refs31–34). Th e order of acidity observed in in -
dividual solven ts is iden tical with th at foun d in oth er solven ts, e.g., in wa-
ter35,36 3.69, 4.16, an d 4.20; in 50% aqueous eth an ol10,24 5.54, 5.66, an d
5.74, respectively. Th e larger acidifyin g effect of th e n aph th alen e skeleton
as com pared with ben zen e is probably due to better stabilization of th e
con jugate base by a m ore exten sive delocalization of its n egative ch arge in
th e n aph th alen e rin g com pared with th e ben zen e rin g.
Th e h igh er acidity of 1-n aph th oic acid as com pared with th at of th e
2-isom er is probably due to lowered coplan arity of carboxylic group an d ar-
om atic rin g as a con sequen ce of th e effect of peri h ydrogen substituen t an d
th us lowered m utual con jugation 1,35,37,38. No such effect can operate in th e
case of 2-n aph th oic acid.
For th e purpose of com parison of differen t effects of th e n aph th alen e an d
ben zen e rin gs on th e dissociation of th e respective carboxylic acid, we
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

Dissociation of Naphthoic Acids
389
m ade use of a com parison of th e series of 3- an d 4-substituted 1-n aph th oic
acids (NA) with th e series of 3- an d 4-substituted ben zoic acids (BA). If th e
3- an d 4-substituted 1-n aph th oic acids are con sidered “pseudom eta” an d
“pseudopara”, respectively, it is possible to use a sim ple lin ear regression
an d correlate th e pKHA values m easured for th ese acids by th e Ham m ett re-
lation , just in an alogy to th e com m on correlation of 3- an d 4-substituted
ben zoic acids. For th is correlation , we used σm,p con stan ts, alth ough th eir
TABLE I
Th e average dissociation con stan ts (pKHA) an d th eir stan dard deviation s (s) of substituted
1-n aph th oic acids in various solven ts at 25 °C
X
MeOH
DMF
Py
AN
EtOH
DMSO
H
8.98(0.02)a 12.00(0.02)a 9.49(0.06)a 20.13(0.01)a 9.87(0.02)
10.63(0.04)
11.29(0.02)
9.85(0.09)
9.82(0.07)
9.22(0.01)
12.05(0.04)
11.22(0.03)
10.95(0.02)
9.97(0.01)
9.97(0.08)
9.14(0.06)
8.95(0.03)
11.34(0.06)
10.66(0.03)
10.11(0.04)
10.02(0.04)
9.69(0.03)
9.68(0.01)
10.62(0.05)
10.24(0.03)
3-NH2
3-Cl
9.16(0.01)
8.42(0.04)
8.50(0.01)
12.47(0.01)
10.98(0.04)
10.95(0.04)
9.80(0.01)
8.72(0.02)
8.63(0.01)
20.63(0.05) 10.10(0.02)
19.67(0.01)
9.22(0.02)
3-Br
19.61(0.02)
9.29(0.02)
3-NO2
4-NH2
8.06(0.01)a 10.35(0.05)a 8.14(0.02)a 19.17(0.02)a 8.76(0.04)
10.33(0.02) 13.82(0.03) 10.90(0.04) 21.65(0.01) 11.32(0.03)
4-OCH3 9.58(0.01)a 12.58(0.05)a 10.15(0.05)a 20.97(0.06)a 10.52(0.01)
4-CH3
4-Cl
9.17(0.03)
12.17(0.01)
9.76(0.02)
20.57(0.01) 10.06(0.02)
8.66(0.04)a 11.31(0.03)a 8.89(0.02)a 19.95(0.06)a 9.42(0.03)
8.68(0.02)a 11.28(0.04)a 8.88(0.03)a 19.91(0.00)a 9.35(0.01)
7.86(0.03)a 10.46(0.02)a 8.07(0.04)a 19.14(0.02)a 8.55(0.01)
4-Br
4-CN
4-NO2
5-NH2
7.75(0.06)
9.13(0.01)a 12.60(0.02)a 9.97(0.03)a 20.36(0.08)a 10.12(0.03)
12.06(0.02) 9.60(0.04) 20.14(0.02) 9.93(0.03)
10.09(0.04)
7.88(0.01)
18.88(0.01)
8.47(0.03)
5-OCH3 9.00(0.02)
5-Cl
8.62(0.02)a 11.31(0.03)a 8.98(0.04)a 19.73(0.07)a 9.39(0.01)
8.58(0.03)a 11.19(0.07)a 8.96(0.08)a 19.80(0.12)a 9.37(0.02)
8.29(0.01)a 10.96(0.02)a 8.90(0.01)a 19.32(0.02)a 9.08(0.02)
8.32(0.04)a 10.86(0.07)a 8.55(0.06)a 19.24(0.08)a 9.09(0.03)
8.38(0.02)a 11.93(0.06)a 9.40(0.04)a 19.70(0.06)a 9.37(0.03)
8.55(0.05)a 10.86(0.07)a 9.23(0.03)a 19.58(0.07)a 9.53(0.03)
5-Br
5-CN
5-NO2
8-Cl
8-NO2
a
Ref.14
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

390
Pařík, Wolfová, Ludwig:
TABLE II
Th e average dissociation con stan ts (pKHA) an d th eir stan dard deviation s (s) of substituted
2-n aph th oic acids in various solven ts at 25 °C
X
MeOHa
DMFa
Pya
ANa
EtOH
DMSO
H
9.36(0.03)
9.39(0.03)
8.87(0.04)
8.85(0.03)
9.03(0.02)
8.82(0.03)
9.54(0.00)
9.44(0.02)
9.13(0.02)
9.13(0.04)
8.77(0.05)
8.73(0.01)
9.59(0.05)
9.39(0.03)
9.41(0.02)
9.10(0.01)
9.10(0.01)
8.88(0.04)
8.79(0.02)
9.49(0.02)
9.32(0.05)
9.11(0.02)
9.07(0.03)
8.86(0.02)
8.85(0.02)
12.11(0.05)
12.26(0.05)
11.24(0.02)
11.20(0.04)
11.66(0.06)
11.40(0.03)
12.47(0.01)
12.31(0.03)
11.99(0.05)
11.87(0.00)
11.49(0.04)
11.37(0.04)
9.74(0.04)
9.89(0.04)
8.98(0.07)
8.98(0.07)
9.29(0.04)
8.98(0.06)
9.95(0.04)
9.87(0.04)
9.39(0.05)
9.39(0.05)
8.99(0.07)
8.86(0.07)
20.30(0.05) 10.15(0.02)
20.52(0.02) 10.26(0.02)
10.85(0.03)
11.00(0.03)
10.00(0.04)
10.04(0.05)
10.42(0.01)
10.23(0.01)
11.11(0.05)
11.02(0.03)
10.68(0.05)
10.64(0.04)
10.17(0.02)
10.13(0.04)
11.42(0.03)
10.98(0.01)
10.98(0.01)
10.56(0.02)
10.57(0.05)
10.32(0.04)
10.18(0.02)
10.84(0.03)
10.91(0.04)
10.34(0.02)
10.36(0.03)
10.07(0.02)
10.11(0.06)
4-CH3
4-Cl
19.73(0.05)
19.76(0.03)
20.20(0.05)
19.94(0.10)
9.61(0.03)
9.56(0.01)
9.73(0.02)
9.48(0.04)
4-Br
5-Br
5-NO2
6-OCH3
6-CH3
6-Cl
20.77(0.01) 10.39(0.03)
20.78(0.04) 10.28(0.01)
20.36(0.05)
20.48(0.01)
19.79(0.05)
19.91(0.06)
9.90(0.03)
9.91(0.02)
9.49(0.04)
9.42(0.03)
6-Br
6-CN
6-NO2
7-NH2
7-OCH3
7-CH3
7-Cl
12.79(0.04) 10.32(0.02)
20.60(0.06) 10.56(0.02)
20.46(0.10) 10.24(0.04)
20.50(0.07) 10.25(0.01)
12.28(0.07)
12.27(0.02)
11.89(0.05)
11.85(0.05)
11.52(0.03)
11.46(0.05)
12.41(0.03)
12.15(0.06)
11.72(0.02)
11.76(0.05)
11.39(0.07)
11.33(0.05)
9.78(0.03)
9.74(0.02)
9.43(0.07)
9.33(0.05)
9.06(0.07)
8.97(0.06)
9.70(0.05)
9.63(0.06)
9.33(0.04)
9.23(0.04)
8.98(0.06)
8.99(0.02)
20.18(0.04)
20.02(0.12)
19.76(0.04)
19.45(0.14)
9.83(0.01)
9.81(0.03)
9.51(0.02)
9.37(0.04)
7-Br
7-CN
7-NO2
8-OCH3
8-CH3
8-Cl
20.47(0.09) 10.44(0.01)
20.46(0.02) 10.18(0.01)
20.32(0.10)
20.32(0.06)
20.05(0.15)
20.01(0.06)
9.93(0.02)
9.95(0.01)
9.64(0.01)
9.63(0.01)
8-Br
8-CN
8-NO2
a
Ref.14
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

Dissociation of Naphthoic Acids
391
application to th e n aph th alen e derivatives description is n ot fully legiti-
m ate. Th e results of th is correlation are presen ted in Table III.
If we com pare th e values of dissociation con stan ts of in dividual an alo-
gous acids, th en alm ost in all th e cases, we can observe h igh er acidity of th e
3- an d 4-substituted 1-n aph th oic acids as com pared with th e correspon din g
ben zoic acids39–41, wh ich is probably caused by th e above-m en tion ed better
stabilization of th e con jugate base th rough a m ore exten sive arom atic sys-
tem . Th is acidifyin g effect of th e n aph th alen e skeleton can be quan tified by
m ean s of th e relation ∆pKH0 A = pKH0 A (NA) – pKH0 A (BA). Th e ∆pKH0 A exh ibit th e
followin g values in th e in dividual solven ts (given in paren th eses): –0.29
(MeOH), –0.31 (DMF), –0.25 (Py), –0.17 (AN), –0.26 (EtOH), –0.35 (DMSO).
Hen ce th e in crease in delocalization of th e n egative ch arge in con jugate
TABLE III
Param eters of lin ear regression s of pKHA vs σm,p of 3- an d 4-substituted 1-n aph th oic acids,
an d 3- an d 4-substituted ben zoic acids in various solven ts
1-Naph th oic acids (NA)
Ben zoic acids (BA)
ρNA/ρBA(s)
Solven t
n
pK0(s)
ρ(s)
s(R)
pK0(s)
ρ(s)
MeOH
DMF
Py
9.10
(0.02)
12.02
(0.04)
9.52
1.71
(0.05)
2.52
0.120
(0.986)
0.192
36
36
36
36
36
36
9.39
1.47
1.16
(0.04)
1.11
(0.08)a
12.33
(0.12)a
9.77
(0.02)a
2.27
(0.08)
2.14
(0.984)
0.113
(0.01)a
2.18
(0.04)
0.98
(0.02)
20.40
(0.02)
9.95
(0.05)
1.90
(0.992)
0.117
(0.06)b
20.57
(0.19)a
10.21
(0.10)a
11.03
(0.04)c
(0.15)b
2.05
(0.07)
0.93
AN
(0.05)
1.94
(0.989)
0.133
(0.01)a
1.66
(0.02)
1.17
EtOH
DMSO
(0.02)
10.68
(0.03)
(0.05)
2.24
(0.987)
0.171
(0.01)a
2.49
(0.03)
0.90
(0.07)
(0.984)
(0.09)c
(0.04)
a
b
c
Ref.39 Calculated from th e publish ed data40 (s = 0.160, R = 0.980, n = 11). Calculated
from th e publish ed data41 (s = 0.145, R = 0.988, n = 21).
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

392
Pařík, Wolfová, Ludwig:
bases due to exten sion of arom atic system wh en goin g from ben zen e to
n aph th alen e is rough ly com parable in all th e m edia used.
Th e order of reaction con stan ts ρ for 1-n aph th oic acids (in creasin g in th e
series: MeOH, AN, EtOH, Py, DMSO, DMF) is rough ly com parable with th at
of ben zoic acids (in creasin g in th e series: MeOH, EtOH, AN, Py, DMF,
DMSO). Hen ce, in both th e series com pared, lower ρ values are foun d in
am ph iprotic MeOH an d EtOH an d in dipolar aprotic protoph obic AN.
Th ese solven ts solvate well th e con jugate base, an d th us decrease th e effect
of substituen t on its stabilization . On th e oth er h an d, h igh er ρ values are
foun d with dipolar aprotic protoph ilic solven ts Py, DMSO, an d DMF,
wh ich , despite th eir good proton -solvation ability, provide a worse stabili-
zation for th e con jugate base an d th us in crease th e im portan ce of
substituen t effects.
An oth er in terestin g fact is th e way in wh ich solvation ch an ges with ex-
ten din g th e arom atic system . If we com pare th e ratios of reaction con -
stan ts, ρ(NA)/ρ(BA), in Table III, we can see a particular im provem en t in
solvation of con jugate bases of 1-n aph th oic acids – as com pared with con -
jugated bases of ben zoic acids – in DMSO an d AN, wh ere th ese ratios are be-
low un ity. Dim eth yl sulfoxide solvates th e carboxylate group worse th an
th e oth er solven ts do; h en ce, th e exten sion of th e arom atic skeleton on go-
in g from ben zen e to n aph th alen e brin gs about a lowerin g of th e reaction
con stan t in th is solven t. Th e in fluen ce of aceton itrile seem s to be sim ilar.
Th e opposite is true for EtOH an d MeOH, an d also DMF, for wh ich th e val-
ues of ratios are above un ity. In th ese solven ts, th e con jugate bases of ben -
zoic acids are solvated better. In pyridin e, th e degrees of solvation of
1-n aph th oic acids an d ben zoic acids appear to be com parable.
In order to com pare th e beh aviour in both th e series of com poun ds, we
also used th e PLS m eth od. Th e m atrix of in depen den t variables X was
form ed by th e pKHA values of ben zoic acids con tain in g th e sam e substitu-
en ts as th e 1-n aph th oic acids m easured in th e sam e solven ts. Th e dim en -
sion s of X m atrix were 12 rows (substrates) an d 6 colum n s (solven ts) an d
were filled to 90% (th e m issin g values were th ose of pKHA of 3-am in o deriv-
ative in MeOH, DMF, Py, AN, an d EtOH, an d th ose of 4-am in o an d 4-cyan o
derivatives in Py). Th e m atrix of depen den t variables, Y, h ad th e sam e di-
m en sion s an d con tain ed th e pKHA values of correspon din g 1-n aph th oic ac-
ids. Th e first laten t variable explain ed 99.04% of variability of th e m atrix of
ben zoic acids (X), wh ile th e exten t of th e explain ed variability by th is first
laten t variable in th e m atrix of 1-n aph th oic acids (Y) was 99.32%. Th e sec-
on d laten t variable turn ed out to be statistically in sign ifican t on th e basis
of F-test. Th e result of calculation in dicates a very close laten t structure of
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

Dissociation of Naphthoic Acids
393
th e data sets an d docum en ts a large degree of sim ilarity in th e acid-base be-
h aviour of 3- an d 4-substituted 1-n aph th oic acids an d 3- an d 4-substituted
ben zoic acids.
CONCLUSIONS
Th e dissociation con stan ts of n aph th oic acids in n on -aqueous m edia m ake
an exten sive set of experim en tal values for study of substituen t effects in
n aph th alen e, an d h en ce th ey were utilized for com parison of effects of th e
ben zen e an d n aph th alen e skeleton s. It was foun d th at 3- an d 4-substituted
1-n aph th oic acids are m ore acidic th an th eir ben zen e an alogues, wh ich is
probably due to a m ore exten sive delocalization of n egative ch arge in th e
con jugate base of n aph th oic acid. It was also foun d th at th e acid-base be-
h aviour of th e acids com pared does n ot sign ifican tly differ from each oth er,
an d so th e n aph th alen e 3α an d 4α position s can rough ly be com pared with
th e ben zen e meta an d para position s, respectively. Clearly, th is fact is due
to th e im possibility of direct con jugation between th e substituen t an d th e
reaction cen tre.
The authors are indebted to Prof. W. Adcock (Flinders University of South Australia, Adelaide,
Australia) who kindly supplied the series of substituted 2-naphthoic acids.
REFERENCES
1. Berliner E., Winicov E. H.: J. Am. Chem. Soc. 1959, 81, 1630.
2. Bonnier J. M., Rinaudo J.: Bull. Soc. Chim. Fr. 1966, 3901.
3. Baliah V., Nadar A. N.: Indian J. Chem. 1971, 9, 671.
4. Fischer A., Murdoch J. D., Packer J., Topsom R. D., Vaughan J.: J. Chem. Soc. 1957, 4358.
5. Fischer A., Mitchell W. J., Ogilvie G. S., Packer J., Packer J. E., Vaughan J.: J. Chem. Soc.
1958, 1426.
6. Fischer A., Fountain H. M., Vaughan J.: J. Chem. Soc. 1959, 1310.
7. Wells P. R., Adcock W.: Aust. J. Chem. 1966, 19, 221.
8. Bryson A.: J. Am. Chem. Soc. 1960, 82, 4862.
9. Wells P. R., Ward E. R.: Chem. Ind. (London) 1958, 528.
10. Wells P. R., Adcock W.: Aust. J. Chem. 1965, 18, 1365.
11. Price C. C., Mertz E. C., Wilson J.: J. Am. Chem. Soc. 1954, 76, 5131.
12. Creamer L. K., Fischer A., Mann B. R., Packer J., Richards R. B., Vaughan J.: J. Org. Chem.
1961, 26, 3148.
13. Hojo M., Katsurakawa K., Yoshida Z.: Tetrahedron Lett. 1968, 1497.
14. Pařík P., Ludwig M.: Collect. Czech. Chem. Commun. 1997, 62, 1737.
15. Ludwig M., Pytela O., Kalfus K., Večeřa M.: Collect. Czech. Chem. Commun. 1984, 49,
1182.
16. Ludwig M., Pytela O., Večeřa M.: Collect. Czech. Chem. Commun. 1984, 49, 2593.
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

394
Pařík, Wolfová, Ludwig:
17. Ludwig M., Pytela O., Večeřa M.: Collect. Czech. Chem. Commun. 1986, 51, 1948.
18. Vondráček M., Večerek B.: Chem. Listy 1955, 49, 772.
19. Vertalier S., Sannié C.: Bull. Soc. Chim. Fr. 1954, 234.
20. Karishin A. P.: Zh. Obshch. Khim. 1963, 33, 2247.
21. Friedlaender P., Weisberg J.: Chem. Ber. 1895, 28, 1838.
22. Luther H., Wächter G.: Chem. Ber. 1949, 82, 161.
23. Haworth R. D., Mavin C. R.: J. Chem. Soc. 1932, 2720.
24. a) Dewar M. J. S., Grisdale P. J.: J. Am. Chem. Soc. 1962, 84, 3541; b) Dewar M. J. S.,
Grisdale P. J.: J. Am. Chem. Soc. 1962, 84, 3546.
25. Shoesmith J. B., Rubli H.: J. Chem. Soc. 1927, 3098.
26. Newman M. S., MacDowell D., Swaminathan S.: J. Org. Chem. 1959, 24, 509.
27. Tsuno Y., Sawada M., Fujii T., Tairaka Y., Yukawa Y.: Bull. Chem. Soc. Jpn. 1975, 48,
3356.
28. Gray G. W., Jones B.: J. Chem. Soc. 1954, 678.
29. Exner O.: Korelačnívztahy v organické chemii. SNTL, Praha 1981.
30. Geladi P., Kowalski B. R.: Anal. Chim. Acta 1986, 185, 1.
31. Kolthoff I. M., Guss L. S.: J. Am. Chem. Soc. 1938, 60, 2516.
32. Kolthoff I. M., Chantooni M. K.: J. Am. Chem. Soc. 1971, 93, 3843.
33. Mukherjee L. M., Shultz R. S.: Talanta 1972, 19, 707.
34. Kolthoff I. M.: J. Phys. Chem. 1931, 35, 2732.
35. Dippy J. F. J., Hughes S. R. C., Laxton J. W.: J. Chem. Soc. 1954, 1470.
36. Bethmann H. G.: Z. Phys. Chem. 1890, 5, 385.
37. Trotter J.: Acta Crystallogr. 1960, 13, 732.
38. Trotter J.: Acta Crystallogr. 1960, 14, 101.
39. Ludwig M., Baron V., Kalfus K., Pytela O., Večeřa M.: Collect. Czech. Chem. Commun.
1986, 51, 2135.
40. Pytela O., Kulhánek J., Ludwig M., Říha V.: Collect. Czech. Chem. Commun. 1994, 59,
627.
41. Kalfus K., Večeřa M.: Collect. Czech. Chem. Commun. 1972, 37, 3607.
Collect. Czech. Chem. Commun. (Vol. 65) (2000)