Selective and eco-friendly procedures for the synthesis of benzimidazole derivatives. The role of the Er(OTf)3 catalyst in the reaction selectivity

Article abstract of DOI:10.3762/bjoc.12.235

An improved and greener protocol for the synthesis of benzimidazole derivatives, starting from o-phenylenediamine, with different aldehydes is reported. Double-condensation products were selectively obtained when Er(OTf)₃ was used as the catalyst in the presence of electron-rich aldehydes. Conversely, the formation of mono-condensation products was the preferred path in absence of this catalyst. One of the major advantages of these reactions was the formation of a single product, avoiding extensive isolation and purification of products, which is frequently associated with these reactions. Theoretical calculations helped to understand the different reactivity established for these reactions. Thus, we found that the charge density on the oxygen of the carbonyl group has a significant impact on the reaction pathway. For instance, electron-rich aldehydes better coordinate to the catalyst, which favours the addition of the amine group to the carbonyl group, therefore facilitating the formation of double-condensation products. Reactions with aliphatic or aromatic aldehydes were possible, without using organic solvents and in a one-pot procedure with short reaction time (2-5 min), affording single products in excellent yields (75-99%). This convenient and eco-friendly methodology offers numerous benefits with respect to other protocols reported for similar compounds.

Full text of DOI:10.3762/bjoc.12.235

Selective and eco-friendly procedures for the synthesis of
benzimidazole derivatives. The role of the Er(OTf)3 catalyst
in the reaction selectivity
Natividad Herrera Cano1, Jorge G. Uranga1, Mónica Nardi2, Antonio Procopio3,
Daniel A. Wunderlin4 and Ana N. Santiago*1,§
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2016, 12, 2410–2419.
1INFIQC-CONICET and Facultad de Ciencias Químicas,
doi:10.3762/bjoc.12.235
Departamento de Química Orgánica, Universidad Nacional de
Córdoba, Ciudad Universitaria, Córdoba, 5000 Argentina,
Received: 18 July 2016
2
Dipartimento di Chimica, Università della Calabria Cubo 12C,
7036-Arcavacata di Rende (CS), Italia, 3Dipartimento di Scienze
della Salute, Università Magna Graecia, Viale Europa,
8100-Germaneto (CZ), Italia and 4ICYTAC-CONICET and Facultad
Accepted: 28 October 2016
Published: 16 November 2016
8
8
This article is part of the Thematic Series "Green chemistry".
Guest Editor: L. Vaccaro
de Ciencias Químicas, Departamento de Química Orgánica,
Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba,
5000 Argentina
©
2016 Herrera Cano et al.; licensee Beilstein-Institut.
Email:
License and terms: see end of document.
Ana N. Santiago* - santiago@fcq.unc.edu.ar
*
Corresponding author
§
Tel: +54 351 5353867, extension 53314
Keywords:
catalysis; charge density; condensation; erbium(III)
trifluoromethanesulfonate; green procedure; heterocycle
Abstract
An improved and greener protocol for the synthesis of benzimidazole derivatives, starting from o-phenylenediamine, with different
aldehydes is reported. Double-condensation products were selectively obtained when Er(OTf)3 was used as the catalyst in the pres-
ence of electron-rich aldehydes. Conversely, the formation of mono-condensation products was the preferred path in absence of this
catalyst. One of the major advantages of these reactions was the formation of a single product, avoiding extensive isolation and
purification of products, which is frequently associated with these reactions.
Theoretical calculations helped to understand the different reactivity established for these reactions. Thus, we found that the charge
density on the oxygen of the carbonyl group has a significant impact on the reaction pathway. For instance, electron-rich aldehydes
better coordinate to the catalyst, which favours the addition of the amine group to the carbonyl group, therefore facilitating the for-
mation of double-condensation products.
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Beilstein J. Org. Chem. 2016, 12, 2410–2419.
Reactions with aliphatic or aromatic aldehydes were possible, without using organic solvents and in a one-pot procedure with short
reaction time (2–5 min), affording single products in excellent yields (75–99%). This convenient and eco-friendly methodology
offers numerous benefits with respect to other protocols reported for similar compounds.
Introduction
The formation of heterocyclic compounds is a very important of 3,3-dimethyl-11-alkyl, or aryl 2,3,4,5-tetrahydro-1H-
task in organic synthesis, mainly because they are present in nu- dibenzo[b,e][1,4]diazepin-1-ones was reported using
merous biologically active compounds and in several natural erbium(III) trifluoromethanesulfonate, Er(OTf)3 as catalyst.
products [1]. Among them the presence of benzimidazole [2-7] The reaction comprises a one-pot condensation between
or benzothiazole [8,9] rings in numerous compounds is an im- o-phenylenediamine and 5,5-dimethylcyclohexane-1,3-dione,
portant structural element for their biological and medical appli- followed by a Er(OTf)3-catalyzed cyclization with diverse
cations. For example benzimidazoles are widely spread in alkyl- or arylcarbonyl chlorides [29,30].
antiulcer, antihypertensive, antiviral, antifungal, anticancer, and
antihistaminic medicines, among others [10-12].
In view of these previous applications, our main goal was the
development of an environmentally friendly synthetic method,
One frequently used protocol for the synthesis of benz- to obtain different derivatives containing the benzimidazole
imidazole derivatives is the coupling of o-phenylenediamines core by a one-pot reaction. Additionally, Er(OTf)3 was selected
with carboxylic acids [13,14]. Another widely used procedure as the catalyst to achieve the selective formation of products in
for the same synthesis represents the condensation of order to avoid tedious work-up and product separation proce-
o-phenylenediamine with aldehydes. The latter approach has dures. Moreover, differences in reactivity were investigated by
become more widely accepted, because of the easy access to a by means of theoretical calculations.
variety of substituted aldehydes. For instance, the reaction be-
tween o-phenylenediamine and benzaldehyde readily affords Results and Discussion
benzimidazole derivatives (Scheme 1). However, the reaction is The benzimidazole core was obtained by air oxidative cyclo-
not selective, affording both 2-substituted (a) and 1,2-di- condensation of o-phenylenediamine with benzaldehyde under
substituted benzimidazoles (b).
different conditions. In water and in the presence of Er(OTf)3,
the diamine and benzaldehyde (1:2 ratio) selectively afforded
Therefore, the main drawbacks of current protocols for the syn- 1-benzyl-2-phenyl-1H-benzimidazole (1b) (72% yield), using
thesis of benzimidazoles include the use of expensive reagents, both microwave irradiation and conventional heating for
difficulties in the preparation of the catalyst, long reaction 15 minutes (Table 1, entries 1 and 3). In the absence of the cata-
times, a narrow scope of substrates, tedious work-up proce- lyst, the same reaction afforded a mixture of products 1a and 1b
dures, the use of hazardous organic solvents and lack of selec- using both conditions. Namely, under microwave irradiation,
tivity [15-21].
41% of 1a and 51% of 1b were formed (Table 1, entry 2).
While, using conventional heating, 52% of 1a and 40% of 1b
Rare earth metals are economical and readily available from were formed (Table 1, entry 4).
commercial sources and represent useful catalysts in organic
synthesis [22]. In particular, erbium(III) promotes environmen- To shorten the reaction time, the catalyzed reaction was carried
tally friendly reactions [23-25], and has been successfully out during 5 minutes at room temperature. Using these last
applied to the synthesis of natural products [26-28]. For conditions, the reaction afforded selectively 1b in 62% yield
instance, an efficient method for the synthesis of a wide range (Table 1, entry 5). On the other hand, when the reaction was
Scheme 1: Formation of the benzimidazole core.
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Beilstein J. Org. Chem. 2016, 12, 2410–2419.
Table 1: Comparison of the efficiency of various catalysts, solvents and temperatures in the reaction of o-phenylenediamine with benzaldehyde.a
Entry
Catalyst
Solvent
Temperature (°C)
Time (min)
Yield (%)
References
1
2
Er(OTf)3
–
H2O
H2O
MW/120b
MW/120b
15
15
72 (1b)c
51 (1b)
this work
this work
41 (1a)
3
Er(OTf)3
–
H2O
H2O
120b
120b
15
15
72 (1b)c
this work
this work
4d
40 (1b)
52 (1a)
5
Er(OTf)3
Er(OTf)3
–
H2O
H2O
H2O
rt
5
5
5
62 (1b)c
74 (1b)c
43 (1b)
this work
this work
this work
6
7
120
120
55 (1a)
8
9
Er(OTf)3
–
ethanol
ethanol
120
120
2
2
91 (1b)
54 (1b)
this work
this work
41 (1a)
1
0
Er(OTf)3
Er(OTf)3
–
–
–
80
80
80
2
2
91 (1b)
90 (1b)
71 (1b)
this work
this work
this work
11e
12
ErCl3·6H2O
15
5
(1a)
1
3
4
5
6
7
8
9
0
1
2
3
4
ErCl3
Yb(OTf)3
Ce(OTf)3
SDS
–
80
80
80
rt
15
60
89 (1b)
70 (1b)
88 (1b)
98 (1b)
99 (1b)
72 (1b)
76 (1b)
90 (1b)
90 (1b)
93 (1b)
87 (1b)
82 (1b)
35 (1a)
this work
this work
this work
[31]
1
1
1
1
1
1
2
2
2
2
2
–
–
H2O
60
22
LaCl3
–
rt
60
[32]
SiO2/ZnCl2
PHP
–
rt
20
[33]
H2O
50
rt
120
60
[15]
HClO4–SiO2
PSSA
ethanol
H2O
[16]
rt
35
[34]
HSO3Cl
TMSCl
2-propanol
H2O
rt
108
300
132
5
[35]
rt
[36]
Amberlite IR-120
Er(OTf)3
ethanol/H2O
H2O
25f
1
[37]
25g
this work
5
0 (1b)
92 (1a)
(1b)
26h,d
–
H2O
1
5
this work
8
27
28
29
30
31
air
air
ethanol
H2O
rt
540
240
5
70 (1a)
58 (1a)
98 (1a)
95 (1a)
66 (1a)
[38]
[39]
[40]
[42]
[42]
100 °C
IBD
dioxane
methanol
methanol
rt
rt
rt
Ru(bpy)3Cl2
Ir(dfppy)2(phen)PF6
120
120
aGeneral reaction conditions: 2 mmol of benzaldehyde and 1 mmol of o-phenylenediamine, 10 mol % of Er(OTf)3 under conventional heating. bThe
reaction mixture was heated in a bath at 120 °C using a closed vessel. cOnly remaining reactants were observed. dAt 40 min the yield of 1b was 54%.
eUnder N2 atmosphere. fUnder sonication. gThe amine/aldehyde molar ratio was 1:1.1. hThe amine/aldehyde molar ratio was 4:1.
carried out at 120 °C during 5 minutes, with and without cata- Next, different solvents were evaluated aiming at increasing the
lyst, product 1b was also formed, with yields of 74% and product yield. When ethanol/water was used as solvent, 1b was
4
3% yield, respectively (Table 1, entries 6 and 7).
formed together with a small amount of product 1a. However,
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Beilstein J. Org. Chem. 2016, 12, 2410–2419.
changing to ethanol as the solvent, the reaction of diamine with 92% of 1a and 8% of 1b were observed using a 4:1 amine/alde-
benzaldehyde at 120 °C selectively afforded 91% of 1b hyde ratio (Table 1, entry 26). This ratio favored the fast cycli-
(
Table 1, entry 8). Conversely, the reaction without catalyst in zation, affording excellent yields of mono-condensation prod-
ethanol afforded a mixture of products 1a (41%) and 1b (54%) uct 1a.
Table 1, entry 9). The highest selectivity towards the double-
(
condensation product 1b was obtained in the reaction without Several reactions between benzaldehyde and o-phenylene-
any solvent at 80 °C. Under these conditions, product 1b could diamine to obtain 2-phenyl-1H-benzimidazole (1a) are known.
be isolated in 91% yield after 2 min reaction time (Table 1, However, they afforded moderate yields requiring longer reac-
entry 10). The use of Er(OTf)3 under a N2 atmosphere did not tion times in the presence of air (Table 1, entries 27 and 28)
change the yield nor the reaction times (Table 1, entry 11). [38,39]. Product 1a was also obtained in a shorter reaction time
Changing the catalyst to ErCl3·6H2O, the reaction afforded 71% using hypervalent iodine as oxidant and dioxane as
1
1
1
b with a small amount (5%) of 1a, after 15 min (Table 1, entry solvent [40,41] or in the presence of [Ru(bpy)3Cl2] or
2). The reaction was more selective using ErCl3 during Ir(dfppy)2(phen)PF6 as catalysts [42] (Table 1, entries 29–31).
5 minutes (Table 1, entry 13). The reaction was also carried The major disadvantage of these methods, however, is the cost
out with other lanthanides such as Yb(OTf)3 and Ce(OTf)3, of these catalysts.
both requiring longer times (60 min) to achieve comparable
product yields (Table 1, entries 14 and 15).
Thus, comparing previous reports with our current method, it is
concluded that the use of Er(OTf)3 as catalyst provides many
Table 1 summarizes these results, comparing our current results advantages over previous ones such as it makes use of an eco-
with other catalysts previously used in the synthesis of nomical, eco-friendly and recyclable catalyst, excellent yields in
benzimidazole derivatives. For instance, the reaction of short reaction times, a simple procedure, short reaction times,
o-phenylenediamine with aromatic aldehydes using sodium and an easy work-up.
dodecyl sulfate (SDS) as the catalyst gave 1b in 98% yield.
However, the yields were low using aliphatic aldehydes In addition to the above mentioned advantages we observed that
together with SDS as catalyst (Table 1, entry 16) [31]. Con- erbium is not involved in the formation of 1a, but it catalyzes
versely, good to moderate yields were observed in reactions be- the formation of 1b. The mechanism for the formation of 1b
tween benzaldehyde and o-phenylenediamine catalyzed by using lanthanum catalysts (LaCl3) was reported by Zhang et al.
lanthanum (LaCl3) [32], SiO2/ZnCl2 [33], polymeric resin- [32]. Considering all the evidences, and the essential role of
bound hexafluorophosphate ion (PHP) [15], perchloric acid Er(OTf)3 on the selectivity between 1a and 1b observed in this
adsorbed on silica gel (HClO4–SiO2) [16], polystyrene sulfonic work, two reaction pathways are proposed and shown in
acid [34], HSO3Cl in 2-propanol [35], trimethylsilyl chloride Scheme 2: (i) through bisimine rearrangement (path i) and (ii)
(
TMSCl) [36], or Amberlite (IR-120) [37]. It is worth mention- through a monoamine cyclocondensation–aminal/immonium re-
ing that these previously reported catalysts required longer reac- arrangement (path ii).
tion times than those used in our current protocol (Table 1,
entries 17–24). Moreover, although other methods are quite In path i, when the aldehyde approaches Er(OTf)3, the carbonyl
satisfactory with regards to reaction yield, many of them were carbon of the aldehyde becomes highly reactive toward the
carried out at high temperatures, or require expensive catalysts. nucleophilic attack of o-phenylenediamine, generating diben-
Furthermore, several previously reported reactions employed zylidenediamine I. Consequently, the 1,2-disubstituted benz-
organic solvents, which are not environmentally friendly. imidazole (b) will be formed through bisimine II, under
Thereby, we propose the use of Er(OTf)3 as catalyst to provide catalytic action of the Lewis acid Er(OTf)3. Thus, the catalyst
an eco-friendly, economical and easy to work-up procedure for acts as an effective electrophilic activating agent for the forma-
the synthesis of 1,2-disubstituted benzimidazoles, which can be tion of the bisimine and promotes the subsequent steps (intra-
afforded in only two minutes.
molecular nucleophilic attack and the following 1,3-hydride
shift), finally affording the 1,2-disubstituted imidazoles (b).
In order to selectively obtain 2-phenyl-1H-benzimidazole (1a),
the reaction was carried out using o-phenylenediamine and In contrast, path ii is a non-catalyzed reaction. In path ii, when
benzaldehyde (1:1.1 ratio) in water, at 1 °C, adding 10 mol % the diamine reacts with the aldehyde, a monoimine III is
Er(OTf)3. Under these conditions, 35% of 2-phenyl-1H-benz- formed. The latter intermediate undergoes an intramolecular
imidazole (1a) and 50% of 1-benzyl-2-phenyl-1H-benz- nucleophilic attack on the C=N, leading to the formation of the
imidazole (1b) were obtained after 5 min reaction (Table 1, imidazoline intermediate IV. This intermediate finally affords
entry 25). When this reaction was performed without catalyst, 2-substituted benzimidazole 1a. Thus, the presence of erbium
2413

Beilstein J. Org. Chem. 2016, 12, 2410–2419.
Scheme 2: Proposed mechanism for the formation of 1,2-disubstituted benzimidazoles b and 2-substituted benzimidazoles a.
determines the reaction pathway (either i or ii), controlling the 4-NO2C6H4CHO and 4-CNC6H4CHO were used, unexpected
selective formation of 1,2-disubstituted vs 2-substituted benz- products were observed (Table 2, entries 7–9). Instead of
imidazole. It is worth to remark that the presence of the carbon- double-condensation products b, the corresponding mono-con-
yl hydrogen in the aldehyde is necessary for the formation of densation products 7a–9a were formed in excellent yields. The
the benzimidazole core. On the contrary, the reaction of the di- same products were obtained in comparable yields without the
amine with ketones affords benzodiazepine as products [29,30]. use of catalyst.
Next, we investigated the general applicability of our method in These results clearly show that the electronic effects of the sub-
the reaction of o-phenylenediamine with several substituted stituents present in the aldehydes play a significant role in the
aldehydes using the optimized conditions towards products 1a reaction pathway. The 1,2-disubstituted benzimidazoles were
or 1b, respectively. For this, the best conditions to selectively obtained when electron-rich aldehydes were used, while
obtain the double-condensation product 1b (Table 1, entry 10) 2-monosubstituted benzimidazoles were obtained from the reac-
were chosen and a family of 1,2-disubstituted benzimidazoles tion with electron-deficient aldehydes under the same condi-
was successfully synthesized. The results are listed in Table 2. tions.
The reactions of o-phenylenediamine with electron-rich To shed light on this observation, we decided to carry out theo-
aldehydes, such as 4-CH3OC6H4CHO, 4-CH3C6H4CHO, retical calculations, using the BPW91 functional at 6-31+G*
CH3CH2CHO, CH3CHO and 4-C6H5-CH2CHO (Table 2, level, as implemented in Gaussian 09 [43]. In order to evaluate
entries 2–6) afforded the corresponding 1,2-disubstituted benz- the effect of the substituent on the reactivity of aldehydes, we
imidazoles 2b–7b in good yields (over 83%) under the opti- used a molecular descriptor based on the electronic properties
mized conditions. However when aldehydes containing of the carbonyl group. These properties could determinate the
electron-withdrawing groups, such as 4-ClC6H4CHO, affinity between the aldehyde and the catalyst.
2414

Beilstein J. Org. Chem. 2016, 12, 2410–2419.
Table 2: Synthesis of 1,2-disubstituted benzimidazoles.a
Entry
R
Time (min)
Product
Yield (%)
1b
Ph
2
91
1b
2c
4-H3COC6H4
2
85
2b
3d
4-CH3C6H4
2
83
3b
4
e
CH3CH2
2
2
96
98
4
b
b
5
f
H3C
5
6
C6H5-CH2
2
97
6
b
a
7g
4-ClC6H4
2–5
78
7
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Beilstein J. Org. Chem. 2016, 12, 2410–2419.
Table 2: Synthesis of 1,2-disubstituted benzimidazoles.a (continued)
8
g
g
4-NO2C6H4
4-CNC6H4
2–5
2–5
79
82
8
a
a
9
9
aGeneral reaction conditions: 1 mmol of benzaldehyde and 0.5 mmol of o-phenylenediamine, 10 mol % of Er(OTf)3 under conventional heating at
0 °C for the indicated time. bWith 9% of 1a. cWith 15% of 2a. dWith 17% of 3a. eWith 4% of 4a. fWith 2% of 5a. gProduct b was not detected. Similar
8
yields were obtained without catalyst.
Geometries were optimized for all aldehydes and electrostatic activity of these aldehydes. The greater the charge density on
potential (ESP) population analyses were done to obtain the the oxygen, the greater the affinity of it to erbium, enabling the
charge density on the carbonyl group. The calculated charge formation of 1,2-disubstituted benzimidazoles (Scheme 2,
density on the oxygen of carbonyl group could indicate the re- path i). As it can be seen from Figure 1, the charge density at
Figure 1: ESP maps and charge density on carbonylic oxygen atoms for the studied aldehydes obtained at the BPW91/6-31+G* level. All maps used
consistent surface potential ranges (−0.05237 (red) to 0.05237 (blue)) and an isovalue of electron density of 0.0004. All values are expressed in
atomic units.
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Beilstein J. Org. Chem. 2016, 12, 2410–2419.
the oxygen of the carbonyl group is a well-suited molecular Next the selectivity towards the mono-condensation products a
descriptor for the behavior of the aldehyde.
was investigated (Table 3) using the best conditions identified
for the synthesis of 2-phenylbenzimidazole (1a, Table 1, entry
Our current results show that the charge density for aldehydes 21). As it can be seen from Table 3, good reaction yields
containing electron-donating or aliphatic groups varies from (>80%) were obtained with aldehydes containing both, electron-
−
0.57 to −0.53, while the corresponding densities for aldehydes donating groups (Table 3, entries 2–6) and electron-with-
containing electron-withdrawing groups were found to be in a drawing groups (Table 3, entries 7-8) at low temperature using
range from −0.52 to −0.51. The aldehydes containing electron- short reactions times. Thus, the new procedure is highly versa-
donating or aliphatic groups show a higher density of tile for the selective synthesis of 2-substituted benzimidazoles
negative charge on the oxygen atom than aldehydes containing of general type a.
electron-withdrawing groups (Figure 1). As a consequence,
electron-rich aldehydes coordinate better with the catalyst, Conclusion
promoting the addition of the amine group to the carbonyl We reported a practical and environmentally friendly one-pot
group, and affording double-substitution products (Scheme 2, method for the simple and selective synthesis of 1,2-di-
path i). Conversely, aldehydes substituted with electron-with- substituted or 2-substituted benzimidazoles, starting from
drawing groups do not coordinate well due to their lower densi- o-phenylenediamine in the presence of aromatic or aliphatic
ty of negative charge on the oxygen atom (Figure 1). In the aldehydes. The use of Er(OTf)3 as commercially available
latter case, the formation of mono-condensation products is and easily recyclable catalyst promoted the synthesis of
favored without the intervention of the catalyst (Scheme 2, 1,2-disubstituted benzimidazoles. Other lanthanides also
path ii). These results are consistent with our experimental catalyzed this reaction but required longer reaction times.
results.
On the other hand, 2-substituted benzimidazoles were selec-
Table 3: Synthesis of 2-substituted benzimidazoles a.a
Entry
R
Time (min)
Product
Yield (%)
92
1b
Ph
2
1a
2a
3a
4a
5a
2
c
4-H3COC6H4
4-CH3C6H4
CH3CH2
2
2
1
1
99
94
96
97
3
d
e
4
5
f
H3C
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Beilstein J. Org. Chem. 2016, 12, 2410–2419.
Table 3: Synthesis of 2-substituted benzimidazoles a.a (continued)
6g
C6H5-CH2
2
91
6a
7a
8a
7
h
h
4-ClC6H4
5
5
81
85
8
4-NO2C6H4
aGeneral reaction conditions: 0.5 mmol of benzaldehyde and 2 mmol of o-phenylenediamine at 1–2 °C in 2–5 minutes without catalyst. bWith 8% of
b. cProduct b was not detected. dWith 5% of 3b. eWith 4% of 4b. fWith 3% of 5b and 7b, respectively. gWith 9% of 6b. hProduct b was not detected.
1
tively obtained in high yield and short reaction times by the Acknowledgements
reaction of phenylenediamine with various aldehydes at low This work was supported in part by the Consejo Nacional de
temperature (1–2 °C) or at 80 °C in case of electron-deficient Investigaciones Cientificas y Técnicas (CONICET), Secretaría
aldehydes.
de Ciencia y Tecnología (SECYT-UNC) and Agencia Nacional
de Promoción Científica y Tecnológica (ANPCyT). NHC grate-
The observed different reactivity, leading to the formation of fully acknowledges receipt of a fellowship from Universita
either mono- or double-condensation products, was explained della Calabria (Italy).
on the basis of calculated charge densities located on the car-
bonyl group that is necessary for the coordination of the cata- References
lyst. We suggest that the calculated charge densities on the
oxygen could indicate the reactivity of these aldehydes. More-
over, the theoretical results predict that a charge density on the
oxygen higher than −0.52 favors the coordination to the cata-
lyst, therefore affording double-condensation products,
which is in full agreement with the experimental results of this
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